Additionally, if you have ever changed your interest, how did you do so?
It's a very odd question but after being interested in what I am currently for 6 years, and something before that for 8, I've realized that I am very obsessive and often lacking in other important areas like basic life skills, self-care, and my own emotional wellbeing. I actually did make a conscious effort to change twice, not because I dislike my interest but because I became worried that my brain would reroute itself to be stuck in the same set of thoughts forever.
I was able to become mildly interested in some other fields, and while doing this tried to break my rigid schedule so I could fit in more daily activities, but in the end I usually revert back to my uncompromising behavior. I've found rather humorously however that while attempting to change my interest, I actually become obsessed with the attempt or nature of obsession itself rather than the interest.
It seems that if we put effort in, we do have a degree of control over what we're interested in, though it usually has to be one thing, and we have to have enough information about the topic to become engaged in it. It has to have variety and be organized, so something like types of cars or chemistry works perfectly because they both follow rules. It also has to have a consistent means of gaining information, for me at least. I've used a combination of science articles and Wikipedia, but if I can't find resources for something and gradually lose interest, I either create my own concepts and articles or I just keep rereading the same material to solve questions I had beforehand, and I think it's a waste of time.