Dollieh Sanctuary

I currently have an unused clear Obitsu 27cm body, and I'm planning on getting a head to be GLaDOS from the game Portal. Currently I'm working on a mockup using some actual head images, but I thought I'd ask for feedback on the design. I don't think there are any stern/frowning looking 27cm doll heads, so I was wondering if there would be any way to mod the lips on an Obitsu head. I've seen resin modded, but not vinyl other than cutting out eyeholes. In regards to eyeholes, is it easier to sculpt lids closed or carve them open? My default is just getting an eyeless head and drawing the eyes on, but there aren't many options of heads for that. Help? (I'll post the updated mockup when I finish it)

EDIT: Here's the mockup! Her hair is supposed to be white but I forgot to make the background transparent.
gladosheadd by Cattya-BJD, on Flickr
IMG_20150417_212409 by Cattya-BJD, on Flickr

I am no expert on Obitsus or vinyl dolls, but I'd say that is way easier to carve eyes open than try to mod them closed - for first, I cannot think any material that could ne used to do it with vinyl head.
For the lips, are you thinking having 3d-shape lips? As based on your design, I'd say if yoo paint eyes why not paint lips too? To my eyes painted on lips would fit better on the style you are having there, and painting them would give you more variation to expressions.

I know WhiteDove has had some success modding vinyl using some sort of caulk, but if you just want the lips to have an expression like in the first pic I see no reason you wouldn't be able to achieve that look with just some carefully applied paint, especially since the obitsu heads have such neutral expressions to begin with.

The best material I know of for modding a vinyl head in terms of adding to it is Red Devil All Purpose Caulk. It's paintable and the times I've used it it's sealed to the vinyl so well that (except for color differences and knowing I did it) I can't tell it wasn't originally part of the sculpt. The bad part is it's almost impossible to get it perfectly smooth (I'm looking into some trick somewhere there that I've missed, still, but more experimentation will be necessary)... I've mostly used it to thicken the jawline on my little old lady Denia (who has wrinkles anyway, of course), and for a burn scar on Summer's leg. She's got old style Barbie click knees, with the scar right near them, and it bends just fine when the knee is clicked with no problems. I've never used it to try to fill in eyeholes on a head (yet), mostly because I've never bought any with open eyeholes.

I will second what people are saying that it'll probably be easier to cut the eyes open than seal them shut, and to give paint a try for the expression first. Obitsu expressions are a lot more neutral than the Barbie heads I've done things to (getting one of those to quit grinning involves a razorblade, superglue, sometimes caulk and sometimes the dremel...)