For precaution, first make a backup of your scene.

This script is used to create a material id node-based. I have used the idea for the compositing scheme that by Olivier Boscournu. My script has helped me to learn some more programming with nodes in blender. 
This Script create a full copy from your scene.

Usage:

1 Open the composer of nodes (in mode: compositing nodes "tree_type") and a text editor panel simultaneously.

2 In the texteditor: press button "new" and copy the script inside, or open .py script, and run it.

3 Press f12 to pull a render and allocate the id.

Usually you're all set for use!.

Sorry for my bad English.
Enjoy!