I'm changing the switch gear on the bike, and as such need a different throttle as it's built into the switch housing.

I'm looking at Japanese switch gear, all of which use the twin cable style of throttle.

Will that work with the single cable on the BMW? I realize the end of the cable would need to be changed.

Read Replacing BMW switches with 'Japanese' ones.  There should be throttle controls with single cable on older models of Japanese motorcycles.

Also read this thread

This thread too. Japanese throttles of the seventies to nineties work on the push-pull principle, mostly because CV-style carbs don't shut off in a hurry when you wack the throttle closed. The newer fly-by-wire and fuel injection systems have gone back to a single cable. The 'close' cable is the one at the rear and you don't need it. The throttle barrel has two cutouts for the cables; the lower one is for the 'open' cable. In truth, it doesn't matter a blind tinker's cuss which cutout you use. Recently I made a throttle cable for LFB which was marginally too long, so I hooked it into the 'close' cutout which solved that problem.

Thanks for those thread links, now ordered a pair of Hayabusa switches on ebay so will use them with the single cable.