I also use GL for a close site. Here's what I did to disable users registrations.
1 - I modified the language file, deleting the option to register
2 - In users.php (around line 810) I made just this modification:
Text Formatted Code
case 'new':
$display .= COM_siteHeader('menu');
// Call custom registration and account record create function
// if enabled and exists
if ($_CONF['custom_registration'] AND (function_exists(custom_userform))) {
$display .= custom_userform('new');
} else {
// $display .= newuserform($msg); <== COMMENTED OUT
$display .= COM_refresh ($_CONF['site_url'] . '/index.php'); <= ADDED
}
$display .= COM_siteFooter();
break;
default:
This way if a user enter ...users.php?mode=new
The page just reloads index.php
An " if " clause using a var in config.php would take 2 minutes to add, and you could toggle registration on and off