I imagine itwill work on a G4 too and it sticks until you rest the nvram.

However..... When I check the CPU count in OSX it shows only one CPU but when I check the count with MorphOS it shows two CPU's still.

I suspect this is because it is passing the boot argument to the OSX kernel rather than disabling it for any OS that is installed.

Any MorphOS devs reading this that could tell us if it's possible (now or at a future date) to disable the 2nd CPU in MorphOS?