This fix works best when you use it on a game where your character has not yet 
been turned into a vampire; your custom race will behave correctly and go 
through the transformation unhindered.

In case your character is already a vampire and you have already activated the
Better Vampires built-in Custom race compatibility option, you should activate
it again from the Better vampires configuration menu; this will cure your 
vampirism and infect you with the disease again. After this is done open the 
console and enter the following command:

set VampireCustomRace to 0

This should prevent you from seeing any duplicate feeding commands and when the
disease transforms you after 3 days you should turn into a vampire again, this 
time with the correct appearance and race.
Note that you could rest 3 days to pass the time while the disease runs it's course.