Thanks for the response, DamianGreda! Your instructions make sense to me, however, after messing around some more, I'm still unable to get my slots to change via midi.
For simplicity, I made my desired performance to be Performance #1 (was previously #2). I'm using my amp in performance mode. If I'm understanding your instructions correctly, that means I should be using Program Change 0-4 to change between all slots in Performance #1. I've tried that all kinds of ways, both through my PreSonus and UM-One interface, but haven't had any luck. It makes me wonder if the Kemper, for some reason, isn't receiving the midi signal, but I don't know of a way to check that.
I currently have my global midi set to omni, but I've also tried it set to specific channels.