Technically, that's true, CobaltDream, but from what I'm experiencing, just using the template as your grid left me with lipstick that either over-ran or didn't quite cover the lip texture.

Wouldn't surprise that I stuffed up somewhere - I have a track record for that - but I've spent ages trying to get this right, and so far I've got:

with the edges deliberately slightly blurred because there again trying to invoke the bias concept to blur edges seemed to move the lipstick mask off-centre with respect to the underlying lip-face texture. I have worked with this so long, and finally gave up, and just slightly blurred the edges instead.

I just know there's a far more elegant solution to this, one that BagginsBill will pull out of his magic bag.

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