I don’t think that, for now at least, you can get a list of all the Input Mapping Contexts (IMCs).
https://docs.unrealengine.com/5.2/en-US/BlueprintAPI/Input/MappingQueries/
But if the Player always uses the same IMC by default and only the “scene” one is specific and you want that to be modular you could promote the IMC that “scene” uses to a variable, expose it and set it like you want on the different “scenes” you have in your world.
On my current project I have setup a way to switch Pawn. Each possessable Pawn has an Actor Component with this logic in it:
In each Pawn I can set up what IMC to use, and since the default Pawn will always use the Default IMC I don’t have to expose this one.
Hope that helps in some way…