Haven’t done it in a while, so I don’t know if the firmware still doesn’t care. But as an experiment, I tried swapping a roll in my AMS mid print. It worked fine. AMS didn’t care if there’s a spool used for the print job until the spool was in use. Printed some black, then had some layers where it wasn’t used and while another filament was printing I swapped the black for orange. When the printer wanted “black” again it happily used the orange spool.
So if you’re clever about how you orient your models, you could print more than 4 colors with the AMS, swapping in a different color when the slot is idle.