Although I love my current one, I am still interested in studying other things too
I just feel like I will regret it if I didn't try it out.
We can only help you out so much here unfortunately. If you won't go into specifics, there really isn't much else we can say but give you what we'd do personally (which can be really unhelpful).
I would suggest drawing up a pro and con table and assigning values to each of the points you make. Or even asking staff/students who work/study the area of discipline about research and what the courses are like, what they learn, and advice on studying it in your own time if it seems like studying it as a course in university is unlikely. Just because you don't study it in university doesn't mean you can't take initiative with your own learning and more peripheral interests, if ya know what I mean. Like sure you won't be able to go into it with as much depth while you're completing your degree, but like you technically
could if it still holds your interest in the years after uni where you won't have to juggle with the studies in your current degree and your mission to learn said-discipline. Unless it's something specialised like archeology or art-curating, which require expert knowledge etc., there's nothing you can't really learn outside of uni. I also really think it's a little bit counter-productive to think about it in the light that 'maybe I'll regret NOT learning it at uni'. You can't do everything - you're only human after all, but it doesn't mean that all the doors for learning are closed after uni. And if you're absolutely sure, you could return to study as a mature student, given you handle the responsibilities that may come after university ie. finding work and planning ahead financially. Don't fret about it.
Another thing you really need to consider is exchange. Personally I'd stick with my degree and see through the exchange, because boy have I heard how amazing exchanges can be, especially because now you've thought ahead and planned it (which is - really - the hard part done and dusted). That's just my opinion.