Ingwe, I just got done totally reshaping a carbelite stock, same stuff I think. Slimmed it way down butt to tip, near ti style. Watch the lungs and eyeballs if you really get into it.
Fiberglass resin is easy to work with, can change contours all you want. There's a Bondo Fiberglass body filler that's likely ideal to work with on these stocks but have not tried it.
When you open up pores, Bondo Glazing spot putty is a good simple way to smooth out, and cheap. Sands easy by hand or orbital. I didn't think there was much shell at all, not like a fully layed-up stock. It's really just sealed with paint or gelcoat I think. Just file, sand, glaze, sand, prime, sand, glaze, sand, prime, paint, repaint, change mind, sand, repaint, repaint...
I learned a bunch here:
http://www.6mmbr.com/stockpainting.html
