Model transplantation

[King Llane]

Is it possible to copy one model's part to another? For example: Paladin's head into Necromancer.
I've tried the way with making the head a helmet and it worked, but the head looked like levitating on some necromancer's Stand animations. Also I want it as single model, not item trick.

 

[Xonok]

This is called a geomerge and is practically the most common way to make models in this community.
As far as I know the levitation problem is most likely to happen if the head doesn't have a bone assigned to it. I'm no expert though, I only do animation transfers and simple MDL editing.