I would like to be able to edit/reschedule a cancelled appointment.

We charge for appointments. Sometimes a customer will cancel the appointment but they want to reschedule at a later date. But they haven't decided when yet! From the shop's perspective, we want to cancel that appointment asap so someone else can book it. But if we cancel it the appointment, we lose the ability to reschedule at a later date. If we create a new appointment as an admin, we lose the custom data that was originally submitted by the customer. And if that customer were to go back and reregister through our website, they would have to pay for another appointment.