I have the same issue to deal with....sketchup was such a good modeling tools and bunch of free 3d models avaliable compare to revit
I don't think there is as the Object Style changes the material for the complete object.
I'm sorry, I'm currently not really fluid in this process, but I've done it already. I believe you can assign different materials to model parts and they are being brought through to Revit (or it was layers, but at that time I had to assign layers to a Maya model for them to be imported as materials to SketchUp, I believe, in order to bring them into Revit).
Anyways, once you have these assigned layers or materials in Revit, you should be able to edit them. The problem is that the materials shown in manage > object styles > imported objects aren't actually the materials assigned to those parts of your model. At least that has been the case in my tests.
Instead, I had to literally go through all of the "Render Material 153-153-153"-Materials that are being generated through the import, color them in some drastic colors to identify them in my model (thanks, Enscape 
) and then adjusted them like I imagined it.
However, this will still not allow you to use actual textures, as Revit doesn't support UV texturing, so any textures you want to apply will be tiled.
It's an incredibly tedious process. I still hope it's going to be a help for you!
once you have these assigned layers or materials in Revit, you should be able to edit them. The problem is that the materials shown in manage > object styles > imported objects aren't actually the materials assigned to those parts of your model. At least that has been the case in my tests.
You have solved the problem from me.At least I found the material that acutally match with the model part instead of changing them in the "object styles"
But still I'm not sure what is the main reason for that
