'local government/LEO gave the all clear' is not a tight defense against federal prosecution and conviction. For instance, Jeremy Kettler was convicted despite full local and state blessing for possession of a silencer in violation of federal law (he, the state, and local government all thought he was following all laws including federal ones, but it turned out federal prosecutor had a different opinion on what 'interstate commerce' is). I personally would never risk getting registered as an offender on the hopes some federal prosecutor has a different view than local LEO, it's just not worth unbanning the guy unless both the state and federal prosecutor have signed statements granting immunity from prosecution.