Second Ball Python!

[Bogertophis]

... The current plan is to thaw one small rat out in a week, offer it to the Spider. So if he doesn't take it I can give it to Loki. But from what I'm told he is an active eater, so I don't think I should be too worried??....

For best results, you want his current home to closely resemble his previous one, and in a 20L, it's a good idea to cover the back & sides with dark paper or poster board
(etc.) for privacy (as well as for heat retention). You'll need to cover the screen top most of the way to retain needed humidity too, but you probably already know that.

Switching to f/t may not come easy, and for best results, don't handle the new snake until he has fed at least 3 times for you (easily & on schedule). For a 2 year-old
snake, he should be eating every other week, so it may be a "while" before you handle him, but while this may be hard for you, it's the best thing for him, as eating is
the most important thing.

Now about your "current plan": you never want to offer prey to a new snake & then give it to your other pet if it's refused. That's a great way to share any diseases
that the new snake might be harboring, & by the way, the new snake should also be quarantined from the other one. Not only should food not be shared, neither should
anything else (like feeding tongs). It's best that they aren't even in the same room & you should be dealing with Loki first, then showering, changing clothes & then dealing with the new snake last, always, to be safer.