That sounds like an effective approach, though for negative identities I would expect a lot of cognitive dissonance at the beginning. If I started telling myself right now that I am an early bird, then while that might become a self-fulfilling prophecy, at first I would have a voice in my head saying "no you're not, look at the evidence". It might be useful to "try on" the identity for a while, e.g. "can I be an early bird for two weeks?". I tried that with vegetarianism, and ended up being a vegetarian for years.