I have heard of cutting a 8 rib to 6, but idk if its frowned upon to go from 10 to 6 rib?

And as far as cutting, just a sharp razor knife and get to it huh?

 

I cut several 12 ribs down to 10 ribs. It works fine. I put a short length of 4x4 in a vice and held a utility blade in it. Then I pulled the belt through the blade while I had someone else keep the belt taught. I was able to keep the cut straight this way.

Or find a 12 rib and split it for two 6 ribs...

 

Ohh yeah I didn't think about making two 6's out of a 12