Do you know anyone who had rewritten his brain to a completely new way.
Say for example, Alan is very emotional and non-funny person ; for whatever reason he wants to be funny and cool guy. Is it possible ? Did anyone able to achieve this ? please dont say that he can fake it, obviously he can but that is not his true nature. He want to change himself by root.
You'd be surprised. A faked behavior can become one's "true nature" if pursued long/intensively enough.
In other words, pushing one's self to be more X (funny etc), even by faking it for some prolonged time, can affect us.
Here's an example (there are better sources, but this came first on a cursory search): forcing a smile can genuinely and measurable make us feel less stressed.
http://www.theatlantic.com/health/archive/2012/07/study-forc...
Lots of the "cool" people you see, including stars, singers etc, is learned cool. A lot of them were as uncool, or even more uncool, as anybody in high school for example -- and "faked till they made it" with regards to being cool, etc.
I'm skeptical of 'true nature' because that seems to preclude change. What matters is the behavior and faking being nice without ever stopping is indistinguishable from actually being nice.
Good luck.