This is the problem (or part of it) -

Displacement isn't going to work because you need the displaced bits to have a transparency and specularity completely seperate from the rest of the skin texture. And the same problem applies with any nodes attached to the skin.

The water drops and rivlets need to be treated as entirely seperate to the underlying skin texture.

And the conforming second-skin aproach I suggested has it own problems when M4/ V4 or whoever, is morphed beyond their standard forms.

It's a knotty problem, but eventually someone much smarter than me will work it out.