Look at the editpad boundary command (Tools > Pad > Boundary)
In reply to Rik Lee:
In reply to David Yackman:
The Pad boundary option is only avaliable in the Allegro license options. It's not there in OrCAD PCB but what you can do is use Tools - Padstack - Modify Design Padstack, then select the Pad. In the Options fold out menu make sure you select Instance so that this edit is only for this pad only (it will rename the padname to padname_1) then click on Edit and change the pad size accordingly in Pad Designer. Once complete use File - Update to Design and Exit and the pad will be replaced.
In reply to steve:
David, a word of caution. If you do not create a padstack that meets your requirements, the next time Gerbers are generated you will have to hand-fix the problem again. When I was in charge of other designers making changes with a Gerber editor was expressly forbiden for this very reason. Your solution works for the short time, I agree, but for the long haul it is a chancy choice.
In reply to BuddSw:
I'm curious as to what the pad shape is that you had to trim? Not terribly important but curious.
I've spent a reasonable part of the last 18 years of my career dealing with power conversion electronics (150kW to 4MW) really high power stuff. Because of the nature of the beast I too have had to deal with many oddball shapes for boards that had nothing to do with reasonable placement or signal flow. You have my sympathies.