Have you ever wanted to reinvent yourself? Start afresh with a new set of qualities and attributes to your character? Have you ever succeeded?
While changing the person you are can, theoretically at least, be done overnight, it's not as simple as it sounds - as you probably know. Yet, nothing physical is stopping it from happening. If you believe humen have a freedom of choice, nothing can prevent you from responding to a stimulus the way your ideal self would, regardless of whether or not that kind of behavior comes naturally.
The easiest way to change who you are is to let it happen with time. This way you can enforce the change you wish to see in your behaviour when you remember to, letting it happen in the background while concentrating on other things. But sometimes you want the change to happen instantly - maybe because the situations demands it or because you're completely fed up with the way things are.
There is a way to change the identity you see yourself possessing immediately.
And that is: change the way you look, the more dramatic the better. And not just clothing. Get a makeover done by a professional, or go get a haircut, or cut your hair yourself. Pluck your eyebrows. Put on bright red lipstick. Anything that changes your appearance immediately and remarkably.
The next time you look at yourself in the mirror you will see a new person. When looking at yourself, do your best to attach your mirror image to your new identity. After that, when a stimulus presents itself, think of the mirror image and how they would respond.
While this technique works right away, you can make the change in who you see yourself to be permanent by repeating this as many times as it takes.