Hi Matthew, I do not see a way to do this, but let’s ask @mary or @wim - they have a better grasp of the dimensioning stuff than I do.
It might be possible as a poor second best, to script the edits you are making.
What application does this for you now?
AutoCAD does not offer the configuration of a separator such as a dash, between the whole inch and the partial inch as you have described. The dash in all CAD applications that I have worked on, always signal the value is going from feet to inches after the dash. I believe that is the standard, and of course, AutoCAD sets the standard. Stacked fraction that are new in Rhino 7 are a good way to show the fractional inch portion different than the whole inch.