Originally Posted by flandroid
Can this hack be UNinstalled from 3.1 by setting update provider to 'hack' and then running the uninstall for the Update Provider hack?
As I understand it, yes, with caveats. The updates-provider uninstaller (which requires 'hack' mode to be enabled beforehand) restores the keys that were installed previously (i.e., the Amazon keys, unless you've been doing something unusual.)
However, it would not delete the key file that was originally installed by the jailbreak
installer (pubhackkey01.pem); that file no longer has any effect on FW 3.1, but in your scenario, it's presumably still present. If you wanted your system to be 100% clean, you'd need to run the jailbreak uninstaller (and uninstallers for any other hacks) before the updates-provider uninstaller.
This stuff is, clearly, getting pretty confusing, and I'd advise people to be extremely cautious about these sorts of modifications - especially given that if you make the wrong move, you risk completely breaking both official and unofficial upgrades.