Folgenden Code suchen:
xtc_db_connect() or die('Unable to connect to database server!');

Danach folgendes Einfügen:
require_once (DIR_FS_INC.'xtc_get_domains.inc.php');
if($http_host = xtc_get_host()){
  $sqlField = xtc_get_sqlField();
  $domain_query = xtc_db_query("select template from " . TABLE_DOMAINS . " where $sqlField = '".$http_host."' and domain_status = '1'");
  if(xtc_db_num_rows($domain_query)){
    $domain = xtc_db_fetch_array($domain_query);
    if(@file_exists('templates/' . $domain['template']))
    define('CURRENT_TEMPLATE', $domain['template']);
  }
}