How to add add/edit tpl for specific content type?

    This might work for you
    <?php
    function <name_of_theme>_preprocess_page(&$variables, $hooks) {
      if ((
    arg(0) == 'node') && (arg(1) == 'add' || arg(2) == 'page')) {
       
    $variables['template_files'][] =  'page-node-add-page';
      }
    }
    ?>
    0