About Exarchates and Themes. I agree that Theme should be used after a limit year, but two Vassals should never change from Exarchate to Theme, as they didn't in real history even after the adoption of the Theme system.
One is the famous Exarchate of Ravenna, name for Venice as Vassal. No reconsiderations about this.
The other is the Exarchate of Africa, and this is something that should be introduced. Respawned Cordoba is a perfect candidate to have this name if vassalized by the Byzantines. But original Cordoba should have the same name as well. Exarchate of Africa was originally conceived as all territories at Western Mediterranean (past the Exarchate of Ravenna to the west), and that not only encompassed Northwestern Africa (capital at Carthage) but the Hispanic possessions too. Spain and Portugal should be more Iberian related Vassal States to Byzantium, but Cordoba could have this African trait, even if not respawned.
These two Exarchates continued to be treated like this even after the introduction of the Theme system as stated {Article Theme (Byzantine district)}: Sicily too was formed as a theme by the end of the century, but the imperial possessions in mainland Italy remained under the exarch of Ravenna or the local doukes, as did Byzantine Africa until the fall of Carthage in 698.
So my suggestion is that, besides Cordoba (Exarchate of Africa) and Venice (Exarchate of Ravenna), all other players should be treated as Exarchates up to something around 630-640 AD, and after that should be treated as Themes. Maybe this could be ignored, as at that date only France could be a candidate for Exarchate, and surely no one would accomplish such a goal (barbs would probably kill most of your poorly trained army before reaching France, at a time that if you really want to win, you wouldn't try this campaign). But it could have the option for fanatic players (I would surely try it out). For the others, no one is spawned before that limit year (the necessity of early war with Arabia makes it impossible to vassalize it before the limit, even if it was at 640 AD). On the other hand Exarchates of Ravenna and Africa should remain with this name for the entire game.
One is the famous Exarchate of Ravenna, name for Venice as Vassal. No reconsiderations about this.
The other is the Exarchate of Africa, and this is something that should be introduced. Respawned Cordoba is a perfect candidate to have this name if vassalized by the Byzantines. But original Cordoba should have the same name as well. Exarchate of Africa was originally conceived as all territories at Western Mediterranean (past the Exarchate of Ravenna to the west), and that not only encompassed Northwestern Africa (capital at Carthage) but the Hispanic possessions too. Spain and Portugal should be more Iberian related Vassal States to Byzantium, but Cordoba could have this African trait, even if not respawned.
These two Exarchates continued to be treated like this even after the introduction of the Theme system as stated {Article Theme (Byzantine district)}: Sicily too was formed as a theme by the end of the century, but the imperial possessions in mainland Italy remained under the exarch of Ravenna or the local doukes, as did Byzantine Africa until the fall of Carthage in 698.
So my suggestion is that, besides Cordoba (Exarchate of Africa) and Venice (Exarchate of Ravenna), all other players should be treated as Exarchates up to something around 630-640 AD, and after that should be treated as Themes. Maybe this could be ignored, as at that date only France could be a candidate for Exarchate, and surely no one would accomplish such a goal (barbs would probably kill most of your poorly trained army before reaching France, at a time that if you really want to win, you wouldn't try this campaign). But it could have the option for fanatic players (I would surely try it out). For the others, no one is spawned before that limit year (the necessity of early war with Arabia makes it impossible to vassalize it before the limit, even if it was at 640 AD). On the other hand Exarchates of Ravenna and Africa should remain with this name for the entire game.