Not really that rigid, I think. Harry. Few people truly have behavior that remains that consistently uniform unless they have the emotional depth of a teaspoon. Most everyone displays traits of both extroversion and introversion around everyone from total strangers to lovers and close friends at different times and in different situations.
I'd probably describe myself as an introvert-I can be (and often am) perfectly content living a solitary life, and often when I am around people it makes me happiest to just stay silent and fade into the wallpaper-but there are also times where I am a mile-a-minute chatterbox without personal space issues, usually when I'm around folks I trust.
Oh, I'm not saying it's rigid. That's why you get people with both tendencies. Extreme introverts are highly distrustful. Extreme extroverts trust people all too readily. Trusting that people will accept you and thus being more confident and interesting as a result is what extroversion is. It's not that you're hardwired to enjoy people more or less, it's something of a state of mind. Much like social anxiety, it's not something you should really celebrate. Instead you should try finding people you like and you feel you can trust. There's nothing in the world like good mates.
The problem with fixing introversion, of course, is that trying to force people to have fun and open up creates perceived feelings of exclusion. If somebody tries to get you to have fun, that means they know you're not having fun to begin with, which signals that you're dragging the atmosphere down, which in turn magnifies the feeling of being alien and unsafe in a social setting. That, or they pity you, which is like being hated except more humiliating because unlike with hatred it means you're both despised and not a plausible threat to anyone.
Or introverts tend toward disliking people because they make them uncomfortable and tired
Introversion isn't something that needs to be fixed.
I'd tend toward the other way around. Nobody hates being accepted and validated, at least not the fact of being such, and nobody likes having to spend time with their shitty cousin who's done time and a whole lot of meth, no matter how extroverted they may seem. Introverts simply have a much wider range of people they can at least imagine being or acting like their shitty meth head cousin. Some of them have very good reasons for doing so - abuse, being ostracized, betrayal - that all make one very readily assume the very worst of people, which leads to shutting oneself off from others.
How you fix that is by putting trust into other people and learning to like them, and if they don't fuck you over you may develop a feeling of safety you haven't had before. It ties into, say, romantic relationships becoming much easier after your first one - the method works, and you have a test case for at least the starting bits (or not, if your relationships have been amazingly fucked up rather than enjoyable). And as I mentioned, the trouble with fixing it conventionally is that you can't force this trust. It's something you have to develop by yourself. The easiest scenario is where somebody lays themselves bare before you without you needing to share anything in return, but that doesn't happen very often. You kind of need to take the first step and hope nobody fucks you over for daring to try.
And then there's the question of what, if anything you need to fix. Do you have no friends and live a lonely existence where you hardly leave the house? You should probably fix that. Do you go out with people you barely know every night to get fucked up beyond all reason and human limitation? Dial up the suspicion. Do you have a couple of friends you like without serious reservations (not like a work friend that you make small talk with despite hating his stupid face and wishing he wasn't such a dick) and can hang out with to cheer yourself up? You're basically fine, congrats!