你可以这样做

  add_filter( \'wp_dropdown_cats\', \'add_yet_another_option\', 10, 2 );

  function add_yet_another_option( $output, $r ){
    $output = str_replace( \'</select>\',\'\',$output ); // remove closing select tag
    $output .= \'<option class="level-0" value="some-value"> Some Custom Options </option>\'; // custom option. 
    $output .= \'</select>\'; // add closing select tag
    return $output;
  }