Creative License

Ok now my question today is When do you change something so much it become something else? If you give a vampire a silver allergy and then give them the ability to change into a different creature like a wolf is it still a vampire? At what point does it become something else? Personally I don't think the story is much fun once something becomes invincible. I mean once there is no danger. Ok maybe if the bad guy is really hard to kill that's one thing but the good guy. Well it loses something. I don't think I can actually answer my own question. I think that if you give someone to many different powers it becomes to hard to define. Even Anita Blake couldn't tell you what she is anymore. Have a nice day.