I've just gotten done downdating iTunes to 10.4.1 on a bunch of Macs.
For starters, you need to boot off another partition so as to delete iTunes 12.2.
After that, things get a little complicated, especially if you want to maintain playcount, ratings and such.
I'm putting together a post as to how I did it for this thread:
iTunes 12.2.
The same methods should work for merely going back to 12.1, or to some version of 11, or a later version of 10.
Oh yes, if you have Time machine going back to an earlier version of the app
and the library, that's likely the easiest route to take.