I have posted a script that applies an overlay to a selected material.

You have the poser python methods manual as a pdf file that comes with Poser.

You need Phils guide or the python documentation for the coding like if-then, for a in b, and so on.

Thats at www.python.org. I think you want version 2.7. 

The detail of how to run a script from a pose file was answered recently by Philc as a reply to me .

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2856324