Warlock pet replacements - How to do it in 4.0?

[Aranx]

Sup, since I'm leecher status, I'm not going to ask you guys to do this edit for me, but I would appreciate some kind of poke in the right direction, if it's even possible after Cataclysm and the added anti-game file changing measures.

I'd like to change my warlock pets into undead pets, since I much prefer the feel of playing a necromancer, rather than a silly demon summoning emokid. The plan is to replace the voidwalker with the armored skeleton model, imp with the WoTLK caster etc etc etc, how do I go about this? What programs do I need?