Well, made some progress on my own. Altering the Fane.lsx file and making a mod of the altered file didn't work. You could change the SupportedRaces to Undead_Elf, and doing so changes Fane to an Undead Elf in character creation. The change is complete both in appearance and abilities. The change also breaks the Listen to Origin Story option.
However, after starting the game Fane reverts to his original existence. The only remaining thing from his brief existence as an Undead Elf, is his Undead Elf portrait.
EDIT: Found a solution, and it was far simpler than I thought. The race is defined by the tags, but origin characters do not have a racial tag, when editing the save file. Obviously they have a racial tag somewhere, but I couldn't find it. Fortunately simply adding a racial tag will make the character that race, in most ways. Adding Elf tag let's you gain memories from flesh eating, and you are referenced as an elf in dialogue, but your original race tag still remains, and sometimes you are called that, and some times you get both options. Origin character tagged dialogue remains, as do undead. But adding Undead_Elf tag on Fane didn't make him an elf. I had to also add an actual Elf tag. Even though custom Undead Elfs make do with just the Undead_Elf tag.
So basically it works, but I don't think I'm brave enough to play the game like this. I don't think there's any danger of bugs of any kind, but I'm worried that this may overrule some origin character dialogues. Although I do get the [Fane] dialogue choices, and my Human tag remains, so there's probably no danger, but I think I'm satisfied with my Mystic, Scholar, Soldier, Nobel, Undead Human Fane.
Last edited by Uriel718; 06/10/17 06:09 PM.