add_action( 'init', 'redirect_login_register' );
function redirect_login_register() {
global $pagenow;
if ( $pagenow == 'wp-login.php' && $_GET['action'] == 'register' ) {
$previous = $_SERVER['HTTP_REFERER'];
wp_redirect( $previous . 'tudominio.com' );
exit();
}
}