In my case I run all sorts of film through my TLRs, I would rather just make an alternate focus mark or scale than tinker with the basic calibration. My Yashica Mat 124g has knob focus with a depth of field scale where one could add a sticker or a stroke of white paint or just visually gauge by one of the existing depth of field indicators.
The ancient Flexaret I have has a swinging lever below the lens on the front for focus. That might be a bit more challenging, but I imagine I could come up with an overlay for the focus scale (if I was actually using the camera!)
Having shot a few rolls with the 124g this past summer, I will say TLRs are nice for IR work since you don't have the opaque filter in the viewfinder path.