Scope

What happens to the MRR for the backdated subscription?

Solution

Since the MRR change has already been recorded for the period in which you made the change, it would not be possible to move or shift the MRR change to a different period or remove or nullify the MRR change.
Even if you do try recreating the subscription change to re-record the MRR (by using the backdating feature as given here the already recorded subscription and MRR change cannot be moved or removed.