Can I edit or delete a single occurrence of a recurring plan?

Yes. On the Schedule tab, tap the day, then tap the plan to open it. To change only that date, tap Edit (the pencil), make your changes, save, and choose Only this date. Changing the Type, title, location, or Notify Me reminder for one date turns that date into its own one-time plan. To remove only that date, tap More (•••), then Delete → Delete This Plan. Your recurring plan stays intact for every other day.