I think it is (or at least was) possible, but extremely messy, time consuming and likely to go wrong, so it is no longer done. The billing engine is in the process of being re-written (though can't recall hearing anything on it for a little while). I don't know it that will allow changes to Direct Debit Dates when that is completed.
Phil
Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.
