This snippet for Drupal 7 is a follow up from this one: Crear formato personalizado para un campo de tipo fecha
In order to implement a settings form to our custom field formatter we only need to use the 'settings' parameter in the field formatter declaration (in hook_field_formatter_info()) and a few hooks.
In this snippet we will mark the obligatory fields present as non-obligatory, and it will be under the condition that the user actually has the role of administrator.