I wouldn't have the first clue how write a Python script.

I think one of the reasons you don't see those MAT files to apply color changes to all skin materials is that the palms and soles never look right. It's okay for slight changes in tone, but not for really dark skin. Because the palms and soles are typically part of the same material zone as the rest of the hand/foot, if not the entire limb.

The OP looks like he's addressed this somehow, though the results don't look natural to me, at least with Genesis.