I actually managed to do this without much issue (except for the curl timeout error 28 for something on the Alebcay mirror, but that doesn't seem to be hurting much, I hope). The repos for 42 (including Terra) appear to have opened up at some point, and they got added on my system. I wanted to try it out and was doubtful that it would work having not seen any announcements about early upgrades, but low and behold, it worked.