Say that I have exported a FaceGenData for my actor. If I make other changes to the actor in CharGen Parts tab without exporting it again, will it override the ones in FaceGenData?

If it does, what's the point of FaceGenData aside from dealing with dark face?

Is it possible to sculpt an actor's face only by using FaceGenData? So I can export a faceGenData from one actor, change its filename, and basically make another actor look precisely like that one?

facegendata is more for the game than the editor. you'll get your unexported changes in the editor, but not in game.

So, let me get this straight:

Assume that I have exported the FaceGenData of Actor "Leeroy" on Monday
When I made changes to Leeroy on Tuesday (say, I made his chin a lot wider), and forgot to export the FaceGenData, when I run Skyrim, I'll still see the Monday version of Leeroy?

What if I have a different actor, Jenkins, with much narrower forehead than Leeroy, exports his FaceGenData, and rename them to overwrite Leeroy's?

Will Leeroy now have Jenkin's face?