it's not really recommended, and depending on what the face up is like and what you're trying to remove. It may not be easy, or pretty when you're done.
You'll also be removing the sealant from one section of the face, exposing that section to more or less yellowing depending on the sealant used. And even because of dirt (a sealed part of the face will pick up dirt than the clean face) will make it look awkward. Resealing would help, but can also cause more issues (with yellowing, chipping, etc) if it's not done properly.
If you are determined to remove a partial face up, then just take winsor newton brush cleaner on a q-tip (damp, not soaking) and scrub away at the part what you're trying to remove. Move carefully and slowly, eventually it should come off clean. Be very careful not to get the brush cleaner ANYWHERE on the face except right where you want it. It almost instantly turns the sealant into sticky goo.
be very careful of blush and contouring on the dolls face, there is not easy way to blend that back in.