What I did when I had Poser 5 and found out how to change that file was to burn a copy of the changed file to the same CD that I had burned my Poser 5 program too.  That way when I installed Poser 5, not only was the program on the CD, but so were the updates, the SN and the library.xml file.  

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi