Everybody needs to watch that movie "What the bleep do we know"
I think that the same concept of changing our attitudes and behaviors. I believe that any outlook or behavior can be changed over time with some work. I don't think that its a good idea for an introvert to suddenly try to go out and try to get out and talk to people and socialize and believe that they are suddenly going to get energy from it if they try hard enough. But if you slowly work on things and change your way of looking at things then your brain will slowly adapt, (just like any other part of the body) and can reconnect itself to react in a different way. I don't think that it would be easy to change from E to I or I to E this way, and most people would not put forward the time and effort to change their perceptions or personality, or whatever. But it is possible. Anything is possible.
I also think that E/I would be easier to change than the other three preferences because there are more accessible ways of doing so.
I'm a very balanced personality so can see different viewpoints of many different people, so that may also be why I think people can just change who they are. Someone of a stronger nature may say "hey, easier said than done, girl!"