[Opserty]

You want to do something like this:

PHP Code:

// $vbulletin->userinfo is the BROWSING user's userinfo 
// You shouldn't overwrite otherwise you will get problems

// Don't include the file extension here
define('THIS_SCRIPT', 'addvb');

require_once('./global.php');
require_once('./includes/class_dm.php');
require_once('./includes/class_dm_user.php'); 

$uid = intval($_GET['uid']);
if(!$uid)
{
    exit('Error: Invalid UserID');
}
else
{
    // Fetch $uid's info
    $userinfo = fetch_userinfo($uid);
    $userdata =& datamanager_init('User', $vbulletin, ERRTYPE_ARRAY);
    // The important bit:
    $userdata->set_existing($userinfo);
    // Overwrite whatever you need to:
    $userdata->set('usergroupid', 2);
    $userdata->save();
}