Hi Timothy,
Thank you for your interest in Syncfusion products.
Based on your information, we suspect that your requirement is to modify the single occurrence in a series using the Recurrence Rule of the appointment. But currently, we do not have such a support to modify the single occurrence.
At the same time, your requirement can be achieved by using Appointment Editor of Schedule. With the help of "Open One" option in recurrence appointment's context menu (i.e. click on any recurrence appointment to view the recurrence context menu), the properties of single occurrence in a series can be modified.
If the above provided information does not meet your scenario, please revert back with some more information regarding your requirement, so that we can provide you the better solution.
Please let us know if you require any further assistance on this.
Regards,
Jeyasri M