IIRC this (or something very similar) has already existed for several years for RDS as an undocumented policy. I forget the exact rules, but you should be able

IIRC this (or something very similar) has already existed for several years for RDS as an undocumented policy. I forget the exact rules, but you should be able to ask an Amazon employee to change your reservation for you as long as it's the same instance type and you're spending at least as much money.