I deal with a lot of multi/sub materials and material IDs on a daily basis. It is painful if there are many sub materials. I really don’t like this process… So, I created a tool which allows you to change all multi/sub material IDs with one click. Also, it shows used material IDs in a scene.
I tested multi/sub , standard or A&G material with mr sky using 3ds max 2013 mental ray. Also, it works proxy objects.
How to use
Drag-and-Drop file onto a view port. The tool will be pop up.
Download Material ID Organizer