I think this is a pretty reasonable request that shouldn’t be too difficult to implement. Some of the belt compositions are pretty terrible while some are outstanding.
For example F6F-5 Hellcat, as someone who prefers stealth belts it would be really nice to not have half of them be useless (iai) immediate action incendiary rounds.
Or in a situation like Swedish aircraft J21A-1, where everything 20mm has a tracer with no option for pure stealth.