I am facing a new problem. You said that c4d.EventAdd() will update the GUI.
I am actually changing the Renderer from plugin which is called using CommandLine. When I make change, the value in drop down for Renderer changes from Standard to Indigo Renderer, but the sub menu doesn't refresh. The submenu has options like Output, Save, Material Override and so on.
When I manually change it back to Standard and again back to Indigo renderer or any, the sub menu is refreshed and respective values are reflected. First it remain same as that of Standard Renderer.
Is there any other way to update render settings menu?