If Byzantine Empire accepts the Union of the Churches, it gets kicked out of its alliance with the Morean Despotate. The event should get Byzantium back into its alliance with Morea and maybe make Morean state religion Catholic also.
Or just get rid of the independent Morea before 1453 thingyTalking about it, the event that cedes Constantinople to the Turks if they capture it and you have Morea should turn your tag to the Morean one.
the 2 brothers than governed Morea where fully independent of BYZ even though one brother , Constantine, became the last Emperor of BYZ.
The other brother , I cannot remember if it was Thomas or demetrius fled to Rome around 1458 and gave his kingdom away to the Ottomans.
So, Morea was not even in alliance with BYZ , but a vassal of the TUR