When I got my tonsils out, I missed the first dose of my stool softener, and the pain meds had me backed up so hard that it felt I was trying to shit a cinder block. Considered going to the ER for a bowel obstruction (which can be super dangerous). Finally passed that first brick, along with a concerning amount of blood, and then what felt like about a half-mile long by three-inch thick poo-choo train that my body had assembled with the help of the stool softener after that first missed dose.
So, between that and diarrhea, I think I'd personally err on the side of diarrhea.
Either way, I'd pay very close attention to how your body responds to any deviations from your medication plan, and make any adjustments in small increments leading up to your post-op appointment where you should discuss them with your doc.