Hi and thanks for your time.
I don´t know if you made reference to the GI Replace Material Switch in Lighting the Environment in Unreal Engine | Unreal Engine 5.1 Documentation
If so, that helps you to change the GI color and make it different from it´s diffuse.
What I want is something like programing little menu in post process maybe or somewhere else wich works for any single material except the ones you add in a list…something like de Override Mat option in 3d max where you specifiy a meterial and exclude objects to oveeride any sinble material in the scene.