Sanguine's codename has been with him ever since her joined Babel. He has not changed it, which could be seen as odd, considering how much of a negative connotation that name has in his mind. It's connected to all of the pain he has caused for others - he was not a good leader back then and much like the canon Doctor - used people under him as pawns more than people. It perfectly matches up with the definition of monsters that Vampire Sarkaz have been described as. Back then he sort of revelled in it and embraced it - picking out the codename Sanguine to reflect it - the color of blood.

But upon waking up from his coma.. He wasn't the same. Granted he still had some fragmented memories from back then but after seeing and hearing what has become of Babel because of him he sort of.. sobers up, and as cliche as it is wants to turn a new leaf. But he decides to keep the codename he used - finding a way for it to reflect his new self, taking more inspiration from the other definition of the word - to stay optimistic and positive, despite the bad situation.

He doesn't abandon it, because at it's core it is who he is - it still is reflective of his sins past, the sins he has to take responsibility for - but in turn allows that codename to become a symbol of who he wants to be first and foremost - someone who wants to give hope to others, no matter what the situation may be.