[Lionel]

The way you have it set, you are making it incompatible with other hacks inserting buddies by wiping it out. Use this instead

$db->query("
UPDATE " . TABLE_PREFIX . "usertextfield
SET buddylist = IF(buddylist <> '', CONCAT(buddylist, ' ', 'YOURADMINID'),
'YOURADMINID')
WHERE userid = '$userid';
");

P.S. I was using the same code you posted all along. Psionic Vision corrected it for me. So the code I posted is his in reality.