[Closed] Accessing Mental Ray

Few Questions:

1. Is there some kind of a command that assigns Mental Ray as
   a default renderer (If it is not allready assigned)?

2. What is the script for setting the Material Override setting
   Enabled/Disabled from the Mental Ray Render Scene Dialog>
   Processing>Material Override

3. If you also know that how could I change the Material to this
   Override-box next to Enabled let me know.

Thanks.