I think that’s your world outliner in the map, right?
So you have the Plot BP, and attached to that, the Mesh BP, which contains the meshes?
Then you can do this kind of thing ( very simplisticly )
but I have no idea about the details. You can tag the meshes, for instance. Or you can record the name of the mesh and the material in the save game ( works from the editor ), but the mesh name might be different next time?
Any help?