@CH23: Most of the incremental KoboUSBMS tweaks I emplemented required touching the startup script.
This requires a full, proper Exit -> Start cycle to take (or a device reboot

).
With a simple KOReader restart, the old startup script keeps being used, and it doesn't know how to deal with the new changes, which at best means it gets caught by the crash handler (i.e., the crash screen), at worst means it gets caught by the USBMS failsafe (i.e., the device shuts down after a while).