You can't brick a New World Mac with incorrect NVRam settings, tho it will seem as if you did.
On tower system, Hold the power button, keep holding, wait for the Boot Chime, Keep holding, wait for the Programers Tone, keep holding, wait for the second Boot Chime, keep holding, finally the screen will light up and you will be presented with Open Firmware with the Defaults loaded rather than whatever you did to hose the system.
Reset the nvram, or change back whatever you changed that hosed the system.
I'll look into how to do this on portables, seem to not work the same.
There will always be a way to load the defaults, tho Apple likely didn't publish this to the general public, so they could turn some coin for there techs.