In an automation script I need to update a ReservationInstance.
For example:
var reservationInstance = new DataMiner.Net.ResourceManager.Objects.ReservationInstance(new TimeRangeUtc(utcStartTime, utcEndTime))
{
ID = bookingGuid,
};

the End property of the reservationInstance is a read only, so how do I change the end time of this existing reservation so it can be updated via the resourceManagerHelper class?

Note: this is not a booking created via the Booking Manager of SRM. It is created via the resourceManagerHelper class:
resourceManagerHelper.AddOrUpdateReservationInstances(reservation);