Vampire dark form can't be changed (eyes, scars etc.)

@SpacyJacobson 

From what you describe, I think you haven't unlinked the two forms of your Vampire when you try to edit them.  To make the human and dark forms of a Vampire different, you have to edit them separately.  Whenever you enter CAS, the two forms of a Vampire are linked by default (same goes for Mermaids).  So if you edit either, you edit both at the same time.  To edit them separately, click on the little chain icon just above the sim's portrait icon so that it is unlinked.  Edit your human form, then click the Vampire dark form portrait and edit the Vampire dark form.  It's pretty much like having two sims as you have to edit everything on each form for Vampires (and Mermaids).

Hope this helps.