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You could manipulate the Appointments collection of the RadScheduler - there are Add/Remove methods. And you could change some properties of the Appointment object in order to update it. You can find more details on this in the provided documentation.
As to your second question, you should go over all appointments and check the whether an appointment is already started. For example you could add a timer object and on each tick of the timer check collection and display your message if the appointment start time is bigger then DateTime.Now.
If you have additional questions feel free to ask.
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