Recurrence handling occurs as follows:
A recurring series of events or todos has a master entry plus entries for exceptions.
Changing the rrules of a single instance returns an error. When rrules are modified for a recurring series, the whole series is deleted and recreated.
Changing dtstart of a recurring series entry causes the whole series to be recreated with the new dtstart, thereby losing all exceptions.
Inserting a rid that was not part of the original rule is not supported.
Multiple rrules for any component are not supported.