You'll find that you're now in the anti-rollback #2 or #3 club. No straightforward way to revert back to last best firmware, I'm afraid. Like all the rest of us: you're stuck. No Limits Dronez did (last time I looked) produce a ' rooted' core board for the mav. 2 that dealt with this and other.... problems .... but at £360 it was too expensive an option to consider. Have you tried approaching whatever controls this airspace to see if they'll grant a waiver in your circumstances? There are other options regarding geofencing, but that depends on whether the NFZ is an airport or military