Hey, this is my latest script tool, calle MatIDTools. I plan to update it with more features while using it, but for now it's already useful (At least for my use).
With this script, you can pick an object with the Multi-Sub Material you want to distribute on scene objects, and after that you can just use the script to select objects and double click on the ID you Want. The script will apply the source material to the selection and add the MaterialID Modifier (Named with the Shader name + ID Number).