You can change it in the mesh properties (affects all identical meshes) or an override in the mesh detail’s panel which affect only the selected mesh(es). I haven’t found the 3rd, where is it? Is it the global override in the lightmass settings? I never use it because I never use the same value for all my meshes.
also, when you start understanding layered materials and vertex painting and you can see the result in real-time, you definitely don’t want to go back to max/vray/corona material creation hehe! It may not be a feature you use everyday in arch-viz but hand-painting water puddles, dust, leaks, dirt is a very satisfying thing 