The only thing I can tell you is that in each player race there is a list of head parts that have check boxes of if they are compatible or not with the race, but it's mostly brows, lips, and ears, however the elven brow is texture based so as long as you're that race you're stuck with it. I know it'll never be like the old days, but I can hope. I miss back in the Fallouts and Oblivion how you could just use Facegen itself with the right programs (loved scanning faces into the game) but now everything seems locked up, but I know Facegen is still behind the scenes so hopefully someone someday will find a way to allow access to facegen data like face parts and charging people's faces less restrictively.
Even creating a character in the CK is annoyingly restrictive when it comes to making their face.
I hate it, I tried to make an elvenish race with a Brenton-like face and elven ears, but it turns out I can't do that because you can't edit that without making a new head mesh (all player races except beast races use the same head model). From what I can tell that part of things are pretty locked down.
