When I use the m4k4 mixer, I generally save it as a new figure, but with any body addons applied, and with the hair once I have that fitting decently.  But the saved name will be different from M4 or V4, just saves me from confusion.

Example: I have one I call Lynn, but I have Lynn 10, Lynn 13, Lynn 16, and Lynn.  Same figure, but with the added morphs and hair fitted so I don't have to mess with them.  Almost the same applies for the M4K4 figures.

However, a mixed figure does not play nice with the fitting room, for whatever reason, I have no idea.  Using Copy Morphs From sometimes does, but it varies with different clothing, some will, some won't.  No thoughts there either. 

Doric

The "I" in Doric is Silent.