I recently had a case with Ivanti Support and currently there is no native way to modify or delete an appointment using an action in a process. I ended up using a SQL trigger on a new collection to modify the existing appointments. The new collection would contain a datetime attribute and at the same time supply the action for my process. The trigger then will process the data from inserted and modify the associated appointment.
My case has been closed and I think I found or created an ER regarding this issue.
Hope it helps!
ModifyAppointments.zip 761 bytes