The can change sprockets but they cant change the transmission, can they? The motors get sealed prior to the season starting, right?
I’m certain they have cassette transmissions. My guess is they probably have assemblies with different ratios ready to bolt right in.
I'd have to check but I think that gear ratios are final when you seal the engine. Cost reduction measures.
You could be right. Maybe it's the smaller classes in GP? Or none of them, I'm not sure. But I seem to recall seeing/hearing that mentioned at some point.
I know the transmission ratios are fixed in WSBK. They can only change sprockets. I remember a video where Rea was bitching about it and the compromises they have to make. Not sure about MotoGP.