Source SDK - Replace Head

Does anyone know how to take a head off one character and replace another characters head with the head of the first character. For example if I wanted to have Breen’s head on Alyx’s body.

you would have to decompile both models, cut the body off the breen model, remove alyx’s head, and then place breen’s head on alyx’s model

then recompile it which is a pain in the ass.