[Simon Lloyd]

Add a required on registration field to the user profile using admincp>user profile fields>add new user profile field.

In a plugin add something like (not tested)

PHP Code:

if ($this->registry->userinfo['fieldx']=='Yes') 
{
$vbulletin->db->query_write(UPDATE " .TABLE_PREFIX."user SET usergroupid = 'XX',
WHERE " .TABLE_PREFIX."user.userid = $this->registry->userinfo['userid']);
} 


replace filedx with the new field number like field8, replace XX with the usergroup that they are getting moved to.

Or you can follow something like this https://vborg.vbsupport.ru/showthread.php?t=251670, seriously, just use the serach function here and you'll find lots