Is there a way to undo it? I activated it hoping it'd be a minimal boost but it just made it so one kill grants the party max level. I deactivated it but the damage was done and now even with the code deactivated my party levels to max immediately.
As for how this happened, I activated it, tested it, saw what the result was and reloaded. I'm guessing I made a mistake in my order of operations though because it stayed active without me knowing while I played through a few tournaments in Olympus. A few saves and savestates later and I've got no backup. Stuck at level 51.
It's my own fault, I guess? I kind of wish there was an explanation on how the code worked (or that instead of "Quick Level Up" it was called like, "Max Level In One Kill." Then I'd have just avoided it.)
Edit: Did some tinkering and fixed the issue myself. I'd delete this post considering how fast I did it, but I think it'd be better to leave it up in case someone makes the same mistake and searches for it.
First after some extrapolation on how the codes worked from the OP, I saw the second half of the code as a value representing the "current amount of experience"
So, first I activated a code that set that value to 0; 2032F210 00000000
Then, I checked my current experience. Sure enough, it was 0. And at level 51, the value to level up was 450378. Yours will be different unless you're also 51.
I took that value, subtracted 1 just to be safe, and then converted 450377 to hex to get 0x6DF49. I made a new code with that value; 2032F210 0006DF49
Loaded up. Checked status. 1 exp to the next level.
Then deactivated the code, saved, killed a heartless, and leveled up to 52. Next level value in my status screen looks normal. So, as far as I can tell, I dug my way out of this hole.