Hiho,
you should found an config.php in the extension folder itself.
Path should be: knowledgeroot/extension/register/config.php
In this config file you can define all what you want.
The default file should be look like this:
<?php
$CONF = array (
"cssfile" => "system/extension/register/extension-register.css",
"enabled" => "1",
"defaultgroup" => "2", // id for the default group - admin: 1, users: 2 (should be default)
"othergroups" => "1,90", // comma seperate list of ids for other groups
"defaultrights" => "220",
"admin" => "0",
"rightedit" => "0",
"theme" => "",
"language" => "en",
"requiredpasswordlength" => "5",
);
?>
So you could change the settings to your need.
Hope this will help.
regards,
Frank