Automatic upgrades stop is only one switch in preferences away. I use it to preserve iOS versions I have to test with. About rollbacks, I'm told that this will

Automatic upgrades stop is only one switch in preferences away. I use it to preserve iOS versions I have to test with. About rollbacks, I'm told that this will leave the baseband modem (not downgradable) in a version not tested with main OS. I can imagine Apple (or any corporation) not willing to support it (if it's true, it seems reasonable, but I really don't know). It can be done, btw, only it's not easy, not for end-users, and, AFAIK, must be planned before upgrade (I know many people that did it).