Hi Doremus. Thanks for the feedback on this. The more I think about it I agree the Pyro mask is not likely to work, and as you say, it could even add contrast. I also agree that controlled flashing can often be used in subtle ways without too much flattening. I was just trying to think out loud about alternatives. But creating the pyro mask (if the stain even ended up doing what I thought it might do) would be exceedingly difficult as I think through each step. So basically the more I thought about it I come to the same conclusions as you.
Regarding development of the original negative, I want to clarify that this thought pertained only to certain (not all) extreme contrast cases, where I try to think about other ways of getting to the final print besides compensating development. So this would fall outside the normal methods of zone system control on the contraction side. I'm able to control these negatives, but just thinking about other possible ways of doing things. Sometimes compensating-type procedures can just end up making things harder due to excessive flattening of values, so occasionally relatively subtle masks can help. Since with practice they can be made to act on specific areas or values, it is sometimes better, even under extreme conditions, to opt for a more mild contraction in the negative.
My interest in masks is limited to this type of situation, so it's not what I would call a standard part of my wokring procedures, just another tool in the box that might help here and there. I'm definitely not trying to put unsharp masks on all my negatives. It's not my cup of tea. But the occasional burn/dodge mask can help.
Thanks again for the response. This is exactly the type of feedback I was hoping to get . I think for now this experiment will go on the back burner.