You’d get the RenderEnvironment, then use SetParameter(“azimuth”, newrotval);
Drag an environment from Rhino to a folder in Windows Explorer so that you get the .renv. Open it in a text editor. You’ll be able to find all parameters you can set. The same you can do with materials and textures, as they are all render contents.
Especially handy when you want to programmatically fiddle with custom RenderContent. This way you don’t need to know the type, nor need access to the class definition.