Finally managed to lock myself out of Qubes.
Decided to add a second monitor. I use a KVM switch to switch between my PC and a work laptop. The second monitor is connected directly to the PC for the time being. After connecting the second monitor, I had trouble booting into Qubes at all; probably because I disconnected the power temporarily (always have boot problems after disconnecting/reconnecting). Finally figured out it was because Secure Boot was somehow re-enabled. I can now get to the login screen, but I lose keyboard and mouse access; which I had set dom0 to automatically allow. I have disk encryption enabled and I have no problem using the keyboard there, so I’m assuming dom0 revoked those permissions, but I’m stumped on why.