Check the Models section and you'll be able to find a few 'fused' models, like a crypt fiends lower body with some other chest, hands and head. So yes it's possible, and you can make an alternate move animation. For each different upper or lower body animation change, you'll have to make a new alternate animation. Watch out with indexed move animation, because if you do that, you'll probably get it to randomly do 1 of those move animations, like every Blizzard model does. I'm not a modeller, so I don't know how to attach animations to certain orders, beside the standard animation like 'attack', 'spell', 'move', 'stand', etc.