the sharing state of the hosted feature service determines who can see and edit it. If you share it with everyone, then everyone will be able to see and edit it. If you only share it with a group, then only members of that group will be able to see and edit it. You can share the feature service with everyone and disable editing. The owner of the item or an admin of the organization can navigate to the item details page of the feature service and click Open>Open with full editing control. This overrides the disabled editing for the owner/admin for that session.
Thanks,
Mike