Sometimes we want to append the activity party list, update particular item in the existing activity party list, or remove specific activity party from the list.
Below is what I discovered on how to do this. Since we can't use the Create/Update/Delete method from the service context on ActivityParty entity, we need to alter the content of the list before attaching to the Activity Field.
In my case I have an ActivityRecipient custom entity that have N:1 to Email entity. Whenever the user add/update/delete this custom entity, the corresponding 'To' recipients gets updated as well.
I use this function in my pre create/update/delete message of my ActivityRecipient entity.
Note: for some reason Recurring Appointment doesn't like Organization Service Context (early bound), therefore we have to use IOrganizationService with Retrieve Request.
Hope this helps,