The script will work on the current selected material. One only, sorry.

The script will disconnect the nodes and reconnect them after inserting the new nodes. Do not manuall do anythingor the script wont find them.

I can amend the script to work on more materials. Can you specify exactly what you need to do ?

If you change the script to point to an image file and a mask it will change the selected texture by overlaying the new image and the old one.