i have no idea why e-on decided to do setup for ambience and diffusion. But i don't have any problem with that because normally i am working on the materials individually anyway. To change the materials for an object which has several materials applied is easy. Open the material window (f6). There you have the list of the used materials for this scene. And there you can start working on the materials without touching the structure of your object(s).

One day your ship comes in - but you're at the airport.