Not a bad idea. Alternatively if that is too complex or requires too many shortcuts, simply “quantize to current grid” would be nice, which is how I do it in Cubase (using the quantize grid value rather than individual shortcuts).
Can I check that I understand the requirement here?
If you’re talking about a shortcut to set the rhythmic grid to a specific value rather than using Alt+[/] to swap between them, that’s already possible.
If you’re talking about requantizing existing music that you’ve played via real-time recording or MIDI import, and you want to requantize to a particular note value without actively opening the Requantize dialog and choosing the new note value, then that is indeed not currently possible.
I’m referring to Preferences > Play > Quantization where one sets specifics for recording input. As far as I know, that’s the only place those values are accessible. It would be so handy to have a few J-shortcuts for quickly changing them.
Although, yes, I’m talking apples and oranges here. One could just as easily record at a semiquaver resolution and then Requantize to quaver.