<?php
 
// which is your Drupal directory? (usually it's in the root (e.g. $_SERVER['DOCUMENT_ROOT']), but it can be different)
$your_drupal_directory = './';
 
 
// store current working directory
$currdir = getcwd();
// change PHP's current directory to Drupal's
chdir($your_drupal_directory);
// including bootstrap file...
require_once("./includes/bootstrap.inc");
 
// http://api.drupal.org/api/drupal/includes%21bootstrap.inc/function/drupal_bootstrap/6
// DRUPAL_BOOTSTRAP_FULL: Drupal is fully loaded, validate and fix input data.
$phase = DRUPAL_BOOTSTRAP_FULL;
drupal_bootstrap($phase);
 
// change PHP's current directory BACK to the original
chdir($currdir);
 
// set the active theme back to default
drupal_set_active_theme_to_default();
 
/**
 * Set the active Drupal themes to default ones
 * Works in Drupal 6, 7 (possibly 8 too)
 *
 * @see http://drupal.stackexchange.com/a/51922/2368
 */
function drupal_set_active_theme_to_default() {
 
  // Provides a list of currently available themes.
  $list_themes = list_themes(TRUE);
  // 6, 7, 8, etc.
  $major_version = (int)VERSION;
 
  $theme_default = isset($list_themes['bartik']) ? 'bartik' : 'garland';
  $admin_theme   = isset($list_themes['seven']) ? 'seven' : 'garland';
 
  // Changes the theme to Garland
  variable_set('theme_default', $theme_default);
 
  // Changes the administration theme to Garland
  variable_set('admin_theme', $admin_theme);
 
  if (module_exists('switchtheme')) {
    if (empty($_GET['theme']) || $_GET['theme'] !== $theme_default) {
      $query = array(
        'theme' => $theme_default
      );
      // in D6, drupal_goto's second argument is the query string, in >=D7, a more general $options array is used
      if($major_version < 7){
        $options = $query;
      }
      else{
        $options = array('query' => $query);
      }
 
      drupal_goto($_GET['q'], $options);
    }
  }
 
  drupal_set_message(t('Default theme has been changed to %theme_default, administration theme has been changed to %admin_theme.', array(
    '%theme_default' => $theme_default,
    '%admin_theme' => $admin_theme
  )));
 
}