1) Deleted the entries from cards.txt that use this old version of the keyword "This creature cannot block":

Aesthir Glider
Ashenmoor Gouger
Bloodghast
Bojuka Brigand
Charging Slateback
Craven Giant
Craven Knight
Daggerclaw Imp
Fallen Askari
Goblin Glider
Goblin Raider
Goblin Rimerunner
Grixis Battlemage
Hagra Crocodile
Hulking Cyclops
Hulking Goblin
Hulking Ogre
Inkfathom Infiltrator
Iron-Barb Hellion
Jamuraan Lion
Jungle Lion
Kyren Glider
Maniacal Rage
Nezumi Cutthroat
Nightshade Stinger
Ogre Taskmaster
Pygmy Pyrosaur
Scavenging Scarab
Shambling Remains
Sluggishness
Spineless Thug
Undying Rage
Villainous Ogre
Yellow Scarves Cavalry
Yellow Scarves General
Yellow Scarves Troops
Young Wei Recruits
2) Converted these 37 cards to use the new form "CARDNAME can't block." and pasted these at the top of file at cards.txt.
3) Searched for and found the old version of the keyword and converted it to the new version in these files:
CardFactory_Auras
CombatUtil

res/cards.txt

@@ -1,3 +1,282 @@
+Aesthir Glider
+3
+Artifact Creature Bird
+no text
+2/1
+CARDNAME can't block.
+Flying
+
+Ashenmoor Gouger
+BR BR BR
+Creature Elemental Warrior
+no text
+4/4
+CARDNAME can't block.
+
+Bloodghast
+B B
+Creature Vampire Spirit
+Bloodghast has haste as long as an opponent has 10 or less life. Landfall - Whenever a land enters the battlefield under your control, you may return Bloodghast from your graveyard to the battlefield.
+2/1
+CARDNAME can't block.
+Landfall
+
+Bojuka Brigand
+1 B
+Creature Human Warrior Ally
+Whenever Bojuka Brigand or another Ally creature enters the battlefield under your control, you may put a +1/+1 counter on Bojuka Brigand.
+1/1
+CARDNAME can't block.
+
+Charging Slateback
+4 R
+Creature Beast
+no text
+4/3
+CARDNAME can't block.
+Morph:4 R
+
+Craven Giant
+2 R
+Creature Giant
+no text
+4/1
+CARDNAME can't block.
+
+Craven Knight
+1 B
+Creature Human Knight
+no text
+2/2
+CARDNAME can't block.
+
+Daggerclaw Imp
+2 B
+Creature Imp
+no text
+3/1
+Flying
+CARDNAME can't block.
+
+Fallen Askari
+1 B
+Creature Human Knight
+no text
+2/2
+Flanking
+CARDNAME can't block.
+
+Goblin Glider
+1 R
+Creature Goblin
+no text
+1/1
+Flying
+CARDNAME can't block.
+
+Goblin Raider
+1 R
+Creature Goblin Warrior
+no text
+2/2
+CARDNAME can't block.
+
+Goblin Rimerunner
+2 R
+Snow Creature Goblin Warrior
+no text
+2/2
+abPumpTgt T:CARDNAME can't block.
+abPump S:Haste
+
+Grixis Battlemage
+2 B
+Creature Human Wizard
+no text
+2/2
+abDrawCards U T:1:Drawback$YouDiscard/1:Draw a card, then discard a card.:Grixis Battlemage - draw a card and discard a card
+abPumpTgt R T:CARDNAME can't block.:Target creature can't block this turn.:Grixis Battlemage - target creature cannot block this turn
+
+Hagra Crocodile
+3 B
+Creature Crocodile
+no text
+3/1
+CARDNAME can't block.
+Landfall - Whenever a land enters the battlefield under your control, CARDNAME gets +2/+2 until end of turn.
+
+Hulking Cyclops
+3 R R
+Creature Cyclops
+no text
+5/5
+CARDNAME can't block.
+
+Hulking Goblin
+1 R
+Creature Goblin
+no text
+2/2
+CARDNAME can't block.
+
+Hulking Ogre
+2 R
+Creature Ogre
+no text
+3/3
+CARDNAME can't block.
+
+Inkfathom Infiltrator
+UB UB
+Creature Merfolk Rogue
+no text
+2/1
+CARDNAME can't block.
+Unblockable
+
+Iron-Barb Hellion
+5 R
+Creature Hellion Beast
+no text
+5/4
+CARDNAME can't block.
+Haste
+
+Jamuraan Lion
+2 W
+Creature Cat
+no text
+3/1
+abPumpTgt W T:CARDNAME can't block.
+
+Jungle Lion
+G
+Creature Cat
+no text
+2/1
+CARDNAME can't block.
+
+Kyren Glider
+1 R
+Creature Goblin
+no text
+1/1
+Flying
+CARDNAME can't block.
+
+Maniacal Rage
+1 R
+Enchantment Aura
+Enchanted creature gets +2/+2 and can't block.
+Enchant creature
+enPump:+2/+2/CARDNAME can't block.
+
+Nezumi Cutthroat
+1 B
+Creature Rat Warrior
+no text
+2/1
+Fear
+CARDNAME can't block.
+
+Nightshade Stinger
+B
+Creature Faerie Rogue
+no text
+1/1
+Flying
+CARDNAME can't block.
+
+Ogre Taskmaster
+3 R
+Creature Ogre
+no text
+4/3
+CARDNAME can't block.
+
+Pygmy Pyrosaur
+1 R
+Creature Lizard
+no text
+1/1
+CARDNAME can't block.
+abPump R:+1/+0
+
+Scavenging Scarab
+3 B
+Creature Insect
+no text
+3/3
+CARDNAME can't block.
+
+Shambling Remains
+1 B R
+Creature Zombie Horror
+no text
+4/3
+CARDNAME can't block.
+Unearth:B R
+
+Sluggishness
+1 R
+Enchantment Aura
+Enchanted creature can't block.
+Enchant creature
+enPumpCurse:CARDNAME can't block.
+When this card is put into a graveyard from the battlefield, return this card to its owner's hand
+
+Spineless Thug
+1 B
+Creature Zombie Mercenary
+no text
+2/2
+CARDNAME can't block.
+
+Undying Rage
+2 R
+Enchantment Aura
+Enchanted creature gets +2/+2 and can't block.
+Enchant creature
+enPump:+2/+2/CARDNAME can't block.
+When this card is put into a graveyard from the battlefield, return this card to its owner's hand
+
+Villainous Ogre
+2 B
+Creature Ogre Warrior
+(NOTE: "As long as you control a Demon, Villainous Ogre has B: Regenerate Villainous Ogre." not implemented.)
+3/2
+CARDNAME can't block.
+
+Yellow Scarves Cavalry
+1 R
+Creature Human Soldier
+no text
+1/1
+Horsemanship
+CARDNAME can't block.
+
+Yellow Scarves General
+3 R
+Creature Human Soldier
+no text
+2/2
+Horsemanship
+CARDNAME can't block.
+
+Yellow Scarves Troops
+1 R
+Creature Human Soldier
+no text
+2/2
+CARDNAME can't block.
+
+Young Wei Recruits
+1 B
+Creature Human Soldier
+no text
+2/2
+CARDNAME can't block.
+
 Ashen Monstrosity
 5 R R
 Creature Spirit
@@ -1776,14 +2055,6 @@ Creature Lizard
 (NOTE: "Spend only mana produced by basic lands to play Imperiosaur." is not implemented.)
 5/5
 
-Hagra Crocodile
-3 B
-Creature Crocodile
-no text
-3/1
-This creature cannot block
-Landfall - Whenever a land enters the battlefield under your control, CARDNAME gets +2/+2 until end of turn.
-
 Junun Efreet
 1 B B
 Creature Efreet
@@ -1856,14 +2127,6 @@ no text
 abPump R:+1/-1
 Unearth:2 B
 
-Shambling Remains
-1 B R
-Creature Zombie Horror
-no text
-4/3
-This creature cannot block
-Unearth:B R
-
 Sedraxis Specter
 U B R
 Creature
@@ -3282,14 +3545,6 @@ Artifact
 no text
 abDrawCards 5 T:2:Drawback$YouDiscard/1:Draw two cards, then discard a card.:Emmessi Tome - draw cards and discard a card
 
-Grixis Battlemage
-2 B
-Creature Human Wizard
-no text
-2/2
-abDrawCards U T:1:Drawback$YouDiscard/1:Draw a card, then discard a card.:Grixis Battlemage - draw a card and discard a card
-abPumpTgt R T:This creature cannot block:Target creature can't block this turn.:Grixis Battlemage - target creature cannot block this turn
-
 Jalum Tome
 3
 Artifact
@@ -3897,13 +4152,6 @@ no text
 2/1
 Swampwalk
 
-Bojuka Brigand
-1 B
-Creature Human Warrior Ally
-Whenever Bojuka Brigand or another Ally creature enters the battlefield under your control, you may put a +1/+1 counter on Bojuka Brigand.
-1/1
-This creature cannot block
-
 Graypelt Hunter
 3 G
 Creature Human Warrior Ally
@@ -3993,14 +4241,6 @@ no text
 Haste
 Cascade
 
-Bloodghast
-B B
-Creature Vampire Spirit
-Bloodghast has haste as long as an opponent has 10 or less life. Landfall - Whenever a land enters the battlefield under your control, you may return Bloodghast from your graveyard to the battlefield.
-2/1
-This creature cannot block
-Landfall
-
 Malakir Bloodwitch
 3 B B
 Creature Vampire Shaman
@@ -6426,14 +6666,6 @@ no text
 Flying
 abPump S S:Shroud
 
-Goblin Rimerunner
-2 R
-Snow Creature Goblin Warrior
-no text
-2/2
-abPumpTgt T:This creature cannot block
-abPump S:Haste
-
 Rimebound Dead
 B
 Snow Creature Skeleton
@@ -6955,13 +7187,6 @@ Creature Human Soldier
 no text
 1/2
 
-Maniacal Rage
-1 R
-Enchantment Aura
-Enchanted creature gets +2/+2 and can't block.
-Enchant creature
-enPump:+2/+2/This creature cannot block
-
 Shield of Duty and Reason
 W
 Enchantment Aura
@@ -8342,22 +8567,6 @@ no text
 1/2
 Horsemanship
 
-Yellow Scarves Cavalry
-1 R
-Creature Human Soldier
-no text
-1/1
-Horsemanship
-This creature cannot block
-
-Yellow Scarves General
-3 R
-Creature Human Soldier
-no text
-2/2
-Horsemanship
-This creature cannot block
-
 Wings of Hope
 W U
 Enchantment Aura
@@ -8398,14 +8607,6 @@ no text
 spGainLife:6
 Draw a card.
 
-Sluggishness
-1 R
-Enchantment Aura
-Enchanted creature can't block.
-Enchant creature
-enPumpCurse:This creature cannot block
-When this card is put into a graveyard from the battlefield, return this card to its owner's hand
-
 Aspect of Mongoose
 1 G
 Enchantment Aura
@@ -8454,14 +8655,6 @@ Enchant creature
 enPump:+2/+0/Trample
 When this card is put into a graveyard from the battlefield, return this card to its owner's hand
 
-Undying Rage
-2 R
-Enchantment Aura
-Enchanted creature gets +2/+2 and can't block.
-Enchant creature
-enPump:+2/+2/This creature cannot block
-When this card is put into a graveyard from the battlefield, return this card to its owner's hand
-
 Vedalken Plotter
 2 U
 Creature Vedalken Wizard
@@ -11741,14 +11934,6 @@ no text
 Flanking
 RegenerateMe:1 B B
 
-Fallen Askari
-1 B
-Creature Human Knight
-no text
-2/2
-Flanking
-This creature cannot block
-
 Femeref Knight
 2 W
 Creature Human Knight
@@ -11890,14 +12075,6 @@ Flying
 Defender
 Wither
 
-Inkfathom Infiltrator
-UB UB
-Creature Merfolk Rogue
-no text
-2/1
-This creature cannot block
-Unblockable
-
 Hearthfire Hobgoblin
 RW RW RW
 Creature Goblin Soldier
@@ -11927,13 +12104,6 @@ Whenever Cold-Eyed Selkie deals combat damage to a player, you may draw that man
 1/1
 Islandwalk
 
-Ashenmoor Gouger
-BR BR BR
-Creature Elemental Warrior
-no text
-4/4
-This creature cannot block
-
 Giant Solifuge
 2 RG RG
 Creature Insect
@@ -12629,14 +12799,6 @@ no text
 Trample
 Morph:G
 
-Charging Slateback
-4 R
-Creature Beast
-no text
-4/3
-This creature cannot block
-Morph:4 R
-
 Crude Rampart
 3 W
 Creature Wall
@@ -13383,13 +13545,6 @@ no text
 1/2
 abPumpTgt T:Forestwalk
 
-Jamuraan Lion
-2 W
-Creature Cat
-no text
-3/1
-abPumpTgt W T:This creature cannot block
-
 Pixie Queen
 2 G G
 Creature Faerie
@@ -15225,14 +15380,6 @@ no text
 0/1
 abPump B:+1/+1
 
-Pygmy Pyrosaur
-1 R
-Creature Lizard
-no text
-1/1
-This creature cannot block
-abPump R:+1/+0
-
 Stone Kavu
 4 G
 Creature Kavu
@@ -16066,138 +16213,6 @@ no text
 6/6
 Unblockable
 
-Aesthir Glider
-3
-Artifact Creature Bird
-no text
-2/1
-This creature cannot block
-Flying
-
-Craven Giant
-2 R
-Creature Giant
-no text
-4/1
-This creature cannot block
-
-Craven Knight
-1 B
-Creature Human Knight
-no text
-2/2
-This creature cannot block
-
-Goblin Glider
-1 R
-Creature Goblin
-no text
-1/1
-Flying
-This creature cannot block
-
-Goblin Raider
-1 R
-Creature Goblin Warrior
-no text
-2/2
-This creature cannot block
-
-Hulking Cyclops
-3 R R
-Creature Cyclops
-no text
-5/5
-This creature cannot block
-
-Hulking Goblin
-1 R
-Creature Goblin
-no text
-2/2
-This creature cannot block
-
-Hulking Ogre
-2 R
-Creature Ogre
-no text
-3/3
-This creature cannot block
-
-Iron-Barb Hellion
-5 R
-Creature Hellion Beast
-no text
-5/4
-This creature cannot block
-Haste
-
-Jungle Lion
-G
-Creature Cat
-no text
-2/1
-This creature cannot block
-
-Kyren Glider
-1 R
-Creature Goblin
-no text
-1/1
-Flying
-This creature cannot block
-
-Nezumi Cutthroat
-1 B
-Creature Rat Warrior
-no text
-2/1
-Fear
-This creature cannot block
-
-Nightshade Stinger
-B
-Creature Faerie Rogue
-no text
-1/1
-Flying
-This creature cannot block
-
-Ogre Taskmaster
-3 R
-Creature Ogre
-no text
-4/3
-This creature cannot block
-
-Scavenging Scarab
-3 B
-Creature Insect
-no text
-3/3
-This creature cannot block
-
-Spineless Thug
-1 B
-Creature Zombie Mercenary
-no text
-2/2
-This creature cannot block
-
-Yellow Scarves Troops
-1 R
-Creature Human Soldier
-no text
-2/2
-This creature cannot block
-
-Young Wei Recruits
-1 B
-Creature Human Soldier
-no text
-2/2
-This creature cannot block
-
 Anaconda
 3 G
 Creature Snake
@@ -18208,14 +18223,6 @@ Legendary Creature Demon Spirit
 At the beginning of each player's upkeep, that player loses 2 life and draws two cards.
 6/5
 
-Daggerclaw Imp
-2 B
-Creature Imp
-no text
-3/1
-Flying
-This creature cannot block
-
 Echoing Decay
 1 B
 Instant
@@ -18251,13 +18258,6 @@ When Keening Banshee comes into play, target creature gets -2/-2 until end of tu
 2/2
 Flying
 
-Villainous Ogre
-2 B
-Creature Ogre Warrior
-(NOTE: "As long as you control a Demon, Villainous Ogre has B: Regenerate Villainous Ogre." not implemented.)
-3/2
-This creature cannot block
-
 Feral Lightning
 3 R R R
 Sorcery

src/forge/CardFactory_Auras.java

@@ -1734,7 +1734,7 @@ class CardFactory_Auras {
                 public void execute() {
                     if(card.isEnchanting()) {
                         Card crd = card.getEnchanting().get(0);
-                        crd.addExtrinsicKeyword("This creature cannot block");
+                        crd.addExtrinsicKeyword("CARDNAME can't block.");
                     }
                 }//execute()
             };//Command
@@ -1747,7 +1747,7 @@ class CardFactory_Auras {
                 public void execute() {
                     if(card.isEnchanting()) {
                         Card crd = card.getEnchanting().get(0);
-                        crd.removeExtrinsicKeyword("This creature cannot block");
+                        crd.removeExtrinsicKeyword("CARDNAME can't block.");
                         
                     }
                     
@@ -2752,7 +2752,7 @@ class CardFactory_Auras {
                         Card crd = card.getEnchanting().get(0);
                         crd.addSemiPermanentAttackBoost(+2);
                         crd.addSemiPermanentDefenseBoost(+2);
-                        crd.addExtrinsicKeyword("This creature cannot block");
+                        crd.addExtrinsicKeyword("CARDNAME can't block.");
                     }
                 }//execute()
             };//Command
@@ -2765,7 +2765,7 @@ class CardFactory_Auras {
                 public void execute() {
                     if(card.isEnchanting()) {
                         Card crd = card.getEnchanting().get(0);
-                        crd.removeExtrinsicKeyword("This creature cannot block");
+                        crd.removeExtrinsicKeyword("CARDNAME can't block.");
                         crd.addSemiPermanentAttackBoost(-2);
                         crd.addSemiPermanentDefenseBoost(-2);
                     }
@@ -5068,7 +5068,7 @@ class CardFactory_Auras {
                         Card crd = card.getEnchanting().get(0);
                         crd.addSemiPermanentAttackBoost(2);
                         crd.addSemiPermanentDefenseBoost(2);
-                        crd.addExtrinsicKeyword("This creature cannot block");
+                        crd.addExtrinsicKeyword("CARDNAME can't block.");
                         
                     }
                 }//execute()
@@ -5084,7 +5084,7 @@ class CardFactory_Auras {
                         Card crd = card.getEnchanting().get(0);
                         crd.addSemiPermanentAttackBoost(-2);
                         crd.addSemiPermanentDefenseBoost(-2);
-                        crd.removeExtrinsicKeyword("This creature cannot block");
+                        crd.removeExtrinsicKeyword("CARDNAME can't block.");
                         
                     }
                     

src/forge/CombatUtil.java

@@ -163,7 +163,7 @@ public class CombatUtil {
         
         if(attacker.getKeyword().contains("Unblockable")) return false;
         
-        if(blocker.getKeyword().contains("This creature cannot block")
+        if(blocker.getKeyword().contains("CARDNAME can't block.")
                 || blocker.getKeyword().contains("This creature can't attack or block")) return false;
         
         if(attacker.getKeyword().contains("Flying")) {