In RhinoScript you will need to dig into RDK scripting. The documentation is very cryptic and not easy to work with, but worth giving it a shot - here is online documentation.
For your use, I modified an example I posted a while ago - try attached and use debugger to look at the parameter lists etc. for materials. The script will also run through all materials in the scene and disable diffuse lighting as well as set the reflectivity @ 0.35.
RDK_RhinoScript_Sample.rvb (1.4 KB)