Easier approach: Make him not a vampire in-game, then set his persondata bits back to being a vampire using SimPE. This way the game does all that heavy lifting and you just need to set one flippy bit.
I am not sure where these persondata bits are, nor how to toggle between vampire and normal. Please elaborate?Eta: I've located persondata 1 and 2 in the extended browser, and vampires have the Persondata 1 value of 4. Is that the only value that I need to change or are there others?