ok, heres the revised script , note this now works on the current material

I have renamed the script to set_image_overlay.py

I have made the specular connect only if it was connected 

the code to set the image nodes are commented out  so remove the # to enable them

after setting the values and filenames

I added a comment line for setting the clamped or tiled setting , its not well documented and for reasons unknown they did not use 0 .

Thanks to Philc for pointing out in his book that the hide preview setting is wrong in the Poser methods manual.

I have commented some things to try to explain whats going on.