SAP SECURITY AUTHORIZATION - SU21 object cannot be edit

Problem adding auth field to auth object (SU21)

When I try to add the field in transaction SU21, I get the message that this is not possible because the object is used in several roles:

1. You will have to remove the object from all the existing roles
2. Then SU21 to amend fields from object
3. Now re-add back the object into existing roles