Hello,  
  
I added a block to minecraft which adds its position to an array in the World.java class. 
In the SpawnerAnimal.java (spawning) class and EntityLiving.java (despawning) I changed the conditions for mob spawning to not just look for a player nearby, but also for the blocks.  
  
The problem is I need to modify named 3 base classes for my mod.  
  
Would it be possible to implement a hook for that? .  
I'm thinking of uses to make automatic mob farms using buildcraft, rp2 (...) without having to stay near the farm. 
  
I'm sorry if the idea is rubbish, but I am completely new to Minecraft modding. 
  
greets marco