I can't speak to the longevity of it, but I've gone ahead and done it on this doll. I applied the Soft Touch over GHSP about three weeks ago, and the head has suffered some abuse as I've dragged it all over the place trying to get it rooted. No damage so far.
It's slightly more "dewy" than I'd like, but I do like the texture. Soft and with just very slight skin texture.
I hesitated a bit because in the world of painting you can paint oil over acrylic, but not acrylic over oil. But since we're sealing over super thinned oil, heat set, on vinyl...It seems like a whole new animal. I read here somewhere that it would be ok. Crossing my fingers