From this UE4-reddit comment , I got the idea of separating head/body for game performance while getting all the shape-key goodies from Manuel Bastioni.
However, is there a way to "cleanly" separate a model without damaging its shape-keys?
(i.e. re-calculate shape-key vertex indexes during separation?)
From what I've seen from some maya-unreal tutorial, messing with shape-key vertex order seems to have hideous effects...