Honestly, people should be able to switch IFFs (so long as they have the rep) at will including shutting down the transponder entirely (none). There is still the session change requirement (for technical reasons), but still. As far as technicality, just use the same code as droprep but put a trigger in an FLHook profile to return x rep to +0.89 when they log back in.
IDs won't rephack you to full rep with the faction that owns the ID because people will use that to farm NPCs without consequence.
Why is there a need for a Miner ID to have its own IFF? Freelancer IFF works fine to make it clear you have no affiliation. Being treated with high suspicion is part of not being affiliated with anyone. You're an unknown, be ready to be treated like an unknown.
IFF stands for Identify Friend or Foe. If they don't have an IFF, you should treat them as a foe as they're not displaying a friendly IFF, until you know them not to be a foe. If you see the Freelancer IFF, you should treat them the same as it is a well known fact that the Freelancer IFF code has fallen into the hands of criminals and they use it to trick people.