Also, if I have a usercontrol that acts as my AdvancedEditTemplate, how would I send the id, or 'key' of that appointment to the usercontrol to use the id?
Following the provided brief description I am not sure that I understand completely the exact goal that you are trying to achieve. I suppose that you have a separate form to fill the data and insert a new Appointment in RadScheduler. Note that the Controls collection of the form contains all controls on the form. Thus, you can find the respective one by name and extract its value. However, if it is not suitable for your case I would kindly ask you to give us more details about the specific requirement that you are trying to achieve. Thus, we would be able to think about a suitable solution and assist you further. Thank you in advance.
I hope this information helps. Should you have further questions I would be glad to help.