I would recommend not hacking up lib-common. Use the system the way that it was designed. GeekLog already has methods in place for implementing customizations. This is done via lib-custom.php. GeekLog also already has methods in place for implementing custom registration forms. Thus, fighting these bots and implementing a black list for registration is as easy as:
1. setting "custom_registration" in config.php to true (line 246)
2. making sure that your template includes ../custom/memberdetail.thtml
3. enhancing the "custom_usercheck" function in lib-custom.php to (starts on line 326):
Text Formatted Code
// fight the porn spammers
$domain = substr(strrchr($email, "@"), 1);
$baned_domains = array('dro4ers.net',
'koziavok.net',
'pornoscop.com',
'4watcher.com',
'strokersclub.net',
'sweetsnet.com',
'1stflirt.org',
'hotmail.com',
'yamy.net',
'lovesnake.net',
'126.com');
if (in_array($domain, $baned_domains))
{
$msg = 'Your email address is hosted on a banned domain. Please resubmit with alternate address.';
}