The Pyrocat-MC formula does not contain KBr.
The primary staining component in Pyrocat-MC is the Catechol (same as Pyrocat-HD).
I doubt that reducing the amount of metol in Pyrocat-MC would reduce the amount of stain. The amount of metol in Pyrocat MC is already small (2.5 grams metol).
If you added Sulfite to the formula, that should reduce the amount of stain (if that's what you're after??).