submitbox unfortunately is not very customizable, and this often requires to delete it and rewrite it.
I've re-written submitbox with the following hook:
* save_label : filter "save" button label to customize #save_post for custom status
* status_display_label : filter status name in #post-status-display
* available_status : filter list of status in #post_status
* available_visibility : filter list of visibilities to show.
* visibility_section : action after visibility section (to add input field as post_password (before OK button)
* publish_label : filter "publish" button label to customize #publish_new_status for custom status
I think this is useful also for other users