Well, I agree with INTJMom that mbti is just a piece of all of it.
With mbti theory, what I gather is that ones' preference - kneejerk response, I suppose - is what isn't going to change, and can't change.
But as far as working on aspects of yourself that you're not happy with, or working to balance things out, as far as I'm concerned, the sky's the limit. I really do think if you have the desire to become more a certain way, it will happen. (I mean, within reason). Doesn't mean your innate preference isn't always going to be there, but your outward response, or net conclusion, could very well change.
For example. Do you want to become more friendly, or outgoing, or more organized, or less organized, or more open, or less open, etc? Well, there are tangible things you can do to work on that. Will it always be rather uncomfortable? Well, probably. It could also be a very unpleasant emotional experience, working on the stuff. But there's nothing saying you can't work on what you perceive as your weaknesses, or things you don't like much about yourself.
Not really tied to mbti (I don't think!) - but by my mid-20's I had become incredibly disillusioned, unhappy, and rather cynical. I hated that I'd become this way, because it was affecting my life and how I viewed pretty much everything. I could have just stayed there, saying, 'Eh, it's just how I am, I'll always be cynical.' But I really didn't think I HAD to stay there. So, I *chose* to work on it. It took about 3 years to do that. And, I truly do feel that I re-wired my brain -- and much of it was a perception change - a way of looking at things, and life, that I hadn't entertained previously. Will my instantaneous response be more on the cynical side? Maybe, but I certainly don't sit there anymore, which is all that matters to me.
On the other hand -- I will **never** ever be a good storyteller, or be the entertainment of a group of people. That is a hopeless endeavor, and it's so completely against who I am, that there's no point in me even trying!! As much as I'd love to be a good storyteller, and am rather envious of those who have that talent!! Sigh..I'll just keep giving my eyes-averted, not terribly descriptive stories that aren't captivating, and there's no changing that.
