Is there a way to resize and re-space already routed differential traces other than re-routing them? I've had to change my stack up late in the game and now need to adjust a large number of already routed differential pairs.
Yes - look under the Route - unsupported prototypes menu for Resize/Respace Diff Pairs then follow the GUI. This won't change Constraint Manager so you can either change that first then run this or vice versa.
I don't see that on my menu, what version are you running?
Allegro PCB Designer 17.2-2016 S042 (so the latest). What do you have?
OrCAD PCB Designer Professional 17.2-2016 S042
You'll need at least an Allegro PCB Designer license to be able to do this. Maybe talk to your channel partner and see if you can get a trial license.