Real quick, this is something that came up recently in the game I'm building and it's more a Quality of Life suggestion more than anything else.
So, to break it down, I have a mod that lets me mark auto-tile walls as 'passable' by assigning it a region number. This basically allows the character to walk behind the wall, adding a bit more 'depth' to the overall design of the level. However, in order to make the lighting work in some spots of this game, I would have had to mark that spot with both one of your designated regions AND mark it with the regions that designate whether a wall is passable or not.
I made a work around that just happens to fit in my game so far where I simply changed the designated region numbers so that 3 is passable and 2 is not, since none of my walls are higher than 2. This allows me to kind of quick and dirty keep the depth aspect of my maps without sacrificing the lighting, but having a second set of lighting region tags that weren't bound to what was passable and what wasn't would actually make my life a whole lot easier and let me have more flexibility in my design. As it stands, anything marked with a height of 2 HAS to be an unpassable tile in order for this combination of systems to work, so I have to design my levels with that in mind.
Simply put, being able to have say, region 2 and region 12 do the same thing as far as lighting is concerned, but allowing 12 to be passable and 2 to be not would give me much more flexibility in my map design. I know this is a very specific thing, but essentially all I am asking is how hard it would be to make a second set of regions that just copy the actions of the original set, I.E. Region 11 = 1, 12 = 2, 13 = 3, etc.
Hopefully that makes sense.