Is it possible to delete, modify, or reactivate a Suppression Rule?
No. Once created, a Suppression Rule cannot be deleted or modified. And once deactivated, a Suppression Rule cannot be reactivated. If you need to make any changes to an active Suppression Rule, you will need to deactivate the active Suppression Rule and create a new one.
Note: deleted Suppression Rules will be automatically deleted after the retention period (by default, 90 days).