Bukkit

I want to make the statics and AI of the mobs world-specific, such as letting cow use default AI in easy survival world (Where I have customized to make survival easier but getting less resources), letting cows use ocelot AI in hard survival world (let cows escape!), and making cows hostile (either to players or to mobs :P) in my Mob-Arena world.
Seen a server made cows attack zombies, but I have another survival world so I can't do that...