is it safe for custom require wp main script

I am second develop a site with wordpress.(only use login/register system).

Because wordpress with a high memory usage, So I am not using the latest wordpress script and use 3.2.1. Then for a further memory save. I modify wordpress main script for require. here is my custom config script.

define('DB_NAME', 'wp');
define('DB_USER', 'root');
define('DB_PASSWORD', 'root');
define('DB_HOST', 'localhost');
define('DB_CHARSET', 'utf8');
define('DB_COLLATE', '');
define('AUTH_KEY',         'some code');
define('SECURE_AUTH_KEY',  'some code');
define('LOGGED_IN_KEY',    'some code');
define('NONCE_KEY',        'some code');
define('AUTH_SALT',        'some code');
define('SECURE_AUTH_SALT', 'some code');
define('LOGGED_IN_SALT',   'some code');
define('NONCE_SALT',       'some code');
define('AUTOSAVE_INTERVAL', 100000000 );
define('WP_POST_REVISIONS', false);
$table_prefix  = 'wp_';
define('WPLANG', '');
define('WP_DEBUG', false);
if ( !defined('ABSPATH') )
	define('ABSPATH', dirname(__FILE__) . '/');
define( 'WPINC', 'wp-includes' );
require( ABSPATH . WPINC . '/load.php' );
require( ABSPATH . WPINC . '/default-constants.php' );
wp_initial_constants( );
wp_check_php_mysql_versions();
@ini_set( 'magic_quotes_runtime', 0 );
@ini_set( 'magic_quotes_sybase',  0 );
date_default_timezone_set( 'UTC' );
wp_unregister_GLOBALS();
wp_fix_server_vars();
require( ABSPATH . WPINC . '/functions.php' );
require( ABSPATH . WPINC . '/class-wp.php' );
require( ABSPATH . WPINC . '/class-wp-error.php' );
require( ABSPATH . WPINC . '/plugin.php' );
require( ABSPATH . WPINC . '/pomo/mo.php' );
require_wp_db();
$GLOBALS['table_prefix'] = $table_prefix;
wp_set_wpdb_vars();
wp_start_object_cache();
function wp_kses_normalize_entities($string) {
	return $string;
}
function wp_logout_url($redirect = '') {
	$args = array( 'action' => 'logout' );
	if ( !empty($redirect) ) {
		$args['redirect_to'] = urlencode( $redirect );
	}

	$logout_url = add_query_arg($args, site_url('wp-login.php', 'login'));
	$logout_url = wp_nonce_url( $logout_url, 'log-out' );

	return apply_filters('logout_url', $logout_url, $redirect);
}
function wp_login_url($redirect = '', $force_reauth = false) {
	$login_url = site_url('wp-login.php', 'login');

	if ( !empty($redirect) )
		$login_url = add_query_arg('redirect_to', urlencode($redirect), $login_url);

	if ( $force_reauth )
		$login_url = add_query_arg('reauth', '1', $login_url);

	return apply_filters('login_url', $login_url, $redirect);
}
function site_url( $path = '', $scheme = null ) {
	return get_site_url(null, $path, $scheme);
}
function get_site_url( $blog_id = null, $path = '', $scheme = null ) {
	// should the list of allowed schemes be maintained elsewhere?
	$orig_scheme = $scheme;
	if ( !in_array( $scheme, array( 'http', 'https' ) ) ) {
		if ( ( 'login_post' == $scheme || 'rpc' == $scheme ) && ( force_ssl_login() || force_ssl_admin() ) )
			$scheme = 'https';
		elseif ( ( 'login' == $scheme ) && force_ssl_admin() )
			$scheme = 'https';
		elseif ( ( 'admin' == $scheme ) && force_ssl_admin() )
			$scheme = 'https';
		else
			$scheme = ( is_ssl() ? 'https' : 'http' );
	}

	if ( empty( $blog_id ) || !is_multisite() )
		$url = get_option( 'siteurl' );
	else
		$url = get_blog_option( $blog_id, 'siteurl' );

	if ( 'http' != $scheme )
		$url = str_replace( 'http://', "{$scheme}://", $url );

	if ( !empty( $path ) && is_string( $path ) && strpos( $path, '..' ) === false )
		$url .= '/' . ltrim( $path, '/' );

	return apply_filters( 'site_url', $url, $path, $orig_scheme, $blog_id );
}
require( ABSPATH . WPINC . '/formatting.php' );
require( ABSPATH . WPINC . '/capabilities.php' );
require( ABSPATH . WPINC . '/query.php' );
require( ABSPATH . WPINC . '/user.php' );
require( ABSPATH . WPINC . '/meta.php' );
wp_cookie_constants( );
require( ABSPATH . WPINC . '/pluggable.php' );
wp_set_internal_encoding();
wp_functionality_constants( );
wp_magic_quotes();
do_action( 'sanitize_comment_cookies' );
$wp_the_query = new WP_Query();
$wp_query = $wp_the_query;
$wp = new WP();
$GLOBALS['wp_roles'] = new WP_Roles();
$wp->init();
do_action( 'init' );
do_action('wp_loaded');

I remove all the unwanted function, like blog, forum, comment, etc. This just for register and login. Then in the main page, use

<?php
include(dirname(__FILE__) .'/costom-config.php');
?>
<!DOCTYPE html>
...

insted of wp_header();

Such a change will save 60% memory for each page load. I want to ask, is it safe for the login/register system? Thanks.