Is there any way to disable Roughness as a quality or feature level switch? Like the Shader Model5 has roughness, but the ES3_1 does not?
In the Shader Complexity visualizer, it appears only using the checkbox “fully rough” will disable roughness for performance
Yes. In the project settings > rendering > rendering overrides you can set some global toggles (including fully rough) based on feature level and quality level.
Actually I can’t find these setting in either of these, is it more an .ini setting?
project settings > rendering
project settings > rendering > rendering overrides
Hey 
@PhosphorArt did you find a solution for this? I am also curious if it is possible to make a material fully rough with a quality switch.
Okay, for some platforms it is possible to set an override for the fully rough option. But unfortunately it is not possible to exclude some materials from this. The only solution I found (without C++) was a editor utlity blueprint that duplicates the original material and enables fully rough on it. Surely not the most elegant solution but a solution.
In case someone has the same problem, here is the pastebin for my utlity script:
If there is some Unreal Dev out here: it would be very helpful to be able to turn on and off fully rough by quality switch. I know this is probably not exposed to reduce the amount of shader permutations but it would be very helpful if someone develops a game for multiple platforms (like we do).