Setting bitmap mapping channel via python

I have an imported model (from archicad), which has all its corresponding material bitmaps set to mapping channel 2.

I’d like to automate setting the channel for all bitmaps to 1 via python. Any pointers would be greatly appreciated!

I’ve been searching but haven’t managed to find a definitive answer.

Perhaps you can piece together enough information via https://jesterking.github.io/rhipy/

Specifically the parts on investigating render content, creating PBR materials with textures, and tweaking textures.