Hmm, I'm not sure why
$db->query("UPDATE `mybb_userfields` SET fid30='default value' WHERE username='".$user_info)['username']."'");
doesn't work. I'll look into this...
I think it's easier to add the query to cron.daily, is this correct? (I want to exclude myself)
UPDATE `mybb_userfields` SET fid30='default value' WHERE fid30='' WHERE ufid!='2'
Oh, whoops, you can't have two WHERE statements. I gtg right now but I'll get back to you.
UPDATE `mybb_userfields` SET fid30='default value' WHERE fid30='' AND ufid!='2'
Maybe.