Disable default registration page in WordPress by redirecting away. Has filter for custom redirection. Used to secure registrations that do not follow standard WordPress registration workflows.

wordpress.disable_registration_.php

add_action('init','disable_default_registration');
function disable_default_registration(){
    global $pagenow;
    if( 'wp-login.php' == $pagenow && $_REQUEST['action'] == 'register') {
        $registration_redirect = apply_filters('disable_default_registration_redirect', site_url());
        wp_redirect($registration_redirect);
        exit();
    }
}