Tried this to see how the options worked. Can't use it to change the default boot obviously, because of HnS, but thought I'd see what it looked like with the booted system suppressed.
Changed the showcurrentOS argument to false, but it's still there in the pop-up list, even after a reboot. Would you expect it to work on an HnS system ?
Also, just for interest, what does the autoreboot do if set to true ? I assume setdefaultonstartup is the one that changes default boot to be the current system.