Depends if it has morphs. If it does it is simple enough. If it doesn't it's a bit more involved. Mil4 is fairly easy to work with, I did one for the M4 beard last night. But it was a lot of playing around for me because I haven't done it for a while.

There are many tutorials out there for doing this that explane it far better then I ever could just google carrara morph target, or check the carraracafe  CarraraCafe | Show, discuss and learn about Carrara 3D

On the other hand Genesis and items that have gone through the autofit are a PITA, or a nut I haven't cracked yet. I know 3DAGE could expalne it so even I could understand, but he seems to be MIA, and I am worried about him.