Want to end date a manager record

Summary:

Have an existing custom manager type defined in lookup PER_SUPERVISOR_TYPE which will no longer be used.

For active person-supervisor records I want to end-date the records (held in per_assignment_supervisors_f).

Using change manager screen, i enter a future date (when i want to end the relationship) and use edit→delete but then get error that when deleting a manager a new manager has to be entered.

So how do I end-date a manager relationship (keeping the relationship record) when I don't want to add a new manager of the same type?

Content (please ensure you mask any confidential information):