Wow I might have find a solution.
Reading through pact_of_steel_2.xml, which is the code of a game that contains a bunch of comments explaining almost every setting and thing you can do in the XML, essentially a guide for TripleA map-makers, I saw this:
carrierCost values: the space this unit takes up when sitting on a carrier. if set to 0 then air units can even land on sea zones without a carrier being present (think sea planes)
Setting carrierCost to 0… I didn’t know that was possible. You can change this value using triggers. A trigger can be used to change this value from 0 to 1 at the start of the Advance Convoys phase. If you have separate aircraft units for every power (e.g. G-fighter, G-bomber, I-fighter, I-bomber), that allows you to only change the values of Italian aircraft on the Italian turn, meaning only the Italian aircraft are not able to land on their turn, and the German aircraft are able to stay in the sea zone! Once it is the German turn, the carrierCost of their aircraft can be set to 1, preventing them to land on their turn. At the start of the Assign Convoy Escorts phase, their carrierCost can be set to 0 allowing them to stay in sea zones again.
Will start working on this and upload it to the Github. If I didn’t miss anything, this should definitely work!
Rolling 10d6:




