Honestly, a region under a TO shouldn't be allowed to change allegiance. Seems like something you'd need actual control of the region to accomplish.
Indirik, the King of Leinster was a Petty King, on par with a Duke, and not the Royalty of England and more conventional nations.
Chenier, you're missing the point. D'hara is no Soviet Union, it is not a state hostile to Terran, has no intentions of becoming hostile to Terran, and barring the current circumstances would likely never become hostile to Terran. Which makes the analogy to Poland-Germany-USSR a poor one in comparison to Britan-France-Germany. And if you want so say fictional, well that invalidates your whole reason for posting a different analogy in the first place. If you want to go fictional well, obviously D'hara is Vermont when Babylon surrendered to it during its war with the Klingon Empire.