The ability for UIT players to change their military if they are - 1000 with the army they are with, but only once via a mission.

+1. With significant cost like Faction Standing Recovery. And possibly an espionage or sabotage mission into your current military's territory.

just make conditions like the bounty hunter.
When you get KOS ye get kicked off from the military program. You need to get back good standing to re apply.

You can add a delay if you want like twice a year or add a fee that increases each time you flip sides 1mil, 2mil , 4mil , 8mil, 16....