@CobaltDream - you're so far ahead of me! Eventually I'll get there, though... right now, just the mechanics of setting up this lip shader is plenty challenging.
Okay, here's my set-up as it stands:

...

and here's Charlotte:

The shininess on her face makes me wonder if I need to connect the rule face node back to Copy Template Skin in the Shader Rules material. Also, looks like I was a bit too generous with the lip fade-out effect ... need to fix that.
Hope no one minds this blow-by-blow, here?

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks