Of course it's possible if the parties agree to it. If the seceding realm isn't willing to forgo this supposed advantage then they're in violation of the rule.
Buffakill, you are clearly horribly ignorant of the specific facts of the case.
There is no way in twelve hells that Enweil would be wiling to accept IVF's neutrality even if IVF were to try to ask for it. They want the city back.