Create Custom Recurrence Window
Click the Create Custom Recurrence Window link to add a new class which defines the appointment recurrence window. The class is a copy of the built-in class used to display the Recurrence Window. The name of the class is a combination of the "CustomRecurrenceWindow" string and a sequential number. The class is a ThemedWindow descendant and you can modify its source code (XAML and codebehind files).
After applying changes, set the OptionsWindows.RecurrenceWindowType value to the custom appointment window type ("CustomRecurrenceWindow1", if you click the smart tag link only once) to display this window instead of the built-in Recurrence Window. You can also handle the SchedulerControl.RecurrenceWindowShowing event and set the event arguments' WindowShowingEventArgs<T>.Window property to the custom recurrence window type.