Replacing default display name to login name
Based on this this answer: add_action( ‘wp_login’, ‘wpse_9326315_format_user_display_name_on_login’ ); function wpse_9326315_format_user_display_name_on_login( $username ) { $user = get_user_by( ‘login’, $username ); $userdata = array( ‘ID’ => $user->ID, ‘display_name’ => $user->user_login, ); wp_update_user( $userdata ); } As soon as they log-in the settings gets changed. So you not only affect new users but also existing ones.