With some wonderful help from Y-Phil, the solution is now tested and working on Mac and Windows, with Poser 11, 12 and 13, and so with both Python 2 and 3.

If anyone is interested in checking it out in earlier version of Poser, I have uploaded the scripts to Free Stuff, and called it "Load Specific Map." If you do, it would be nice if you would leave a comment about your results.