I needed to be able to copy the wp_options table(s) to my development environment as they contain configurations that are needed. To overcome the issue of not being able to set the WP_SITEURL and WP_HOME values in WordPress MultiSite, I wrote a custom filter to replace the _config_wp_siteurl() and _config_wp_home() functions that are available for non-multisite installs that is included in a plugin that is available network-wide and is configured in wp-config.php. I am then able to copy all of the database tables except wp_site and wp_blogs to a local database.

I highly recommend the URL Token Replacement Techniques for WordPress 3.0 article by Chris Murphy to help handle URLs in your content.

This example assumes a subdomain multisite install, with a domain of example.com and two subdomains, www.example.com and second.example.com. The local development URLs will be www.example.local and second.example.local respectively.

WordPress Multisite Updates

Database Changes:

Update the domain value in wp_site:

UPDATE wp_site
SET domain = 'example.local'
WHERE domain = 'example.com';

Update the domain value(s) in wp_blogs:

UPDATE wp_blogs
SET domain = 'www.example.local'
WHERE domain = 'www.example.com';
UPDATE wp_blogs
SET domain = 'second.example.local'
WHERE domain = 'second.example.com';

Plugin Code:

The following plugin should be installed network-wide.

<?php
/*
Plugin Name: MultiSite WP_HOME and WP_SITEURL
Plugin URI: http://doublesharp.com/
Description: Allows wp_options values to be overwritten in wp-config.php for MultiSite
Author: Justin Silver
Version: 1.0
Author URI: http://doublesharp.com
License: GPL2
*/

/**
 * Replace this site's WP_SITEURL URL based on constant values
 *
 * @param String  $url - The original URL
 * @return String - The replaced URL if overridden in wp-config.php
 */
function _ms_config_wp_siteurl( $url = '' ) {
    if (is_multisite()):
        global $blog_id, $current_site;
        $cur_blog_id = defined( 'BLOG_ID_CURRENT_SITE' )?
            BLOG_ID_CURRENT_SITE :
            1;
        $key = ( $blog_id!=$cur_blog_id )? $blog_id.'_' : '';
        $constant = 'WP_'.$key.'SITEURL';
        if ( defined( $constant ) )
            return untrailingslashit( constant($constant) );
    endif;
    return $url;
}
add_filter( 'option_siteurl', '_ms_config_wp_siteurl' );

/**
 * Replace this site's WP_HOME URL based on constant values
 *
 * @param String  $url - The original URL
 * @return String - The replaced URL if overridden in wp-config.php
 */
function _ms_config_wp_home( $url = '' ) {
    if (is_multisite()):
        global $blog_id;
        $cur_blog_id = defined( 'BLOG_ID_CURRENT_SITE' )?
            BLOG_ID_CURRENT_SITE :
            1;
        $key = ( $blog_id!=$cur_blog_id )? $blog_id.'_' : '';
        $constant = 'WP_'.$key.'HOME';
        if ( defined( $constant ) )
            return untrailingslashit( constant($constant) );
    endif;
    return $url;
}
add_filter( 'option_home',    '_ms_config_wp_home'    );
?>

Configure wp-config.php:

Add new constants to wp-config.php. The primary site should use the standard WP_HOME and WP_SITEURL and the tertiary URLs should use WP_{$blog_id}_HOME and WP_{$blog_id}_SITEURL where {$blog_id} is the numeric blog ID value that you want to replace from the wp_blogs table.

define('WP_HOME',      'http://www.example.local');
define('WP_SITEURL',   'http://www.example.local');
define('WP_2_HOME',    'http://secondary.example.local');
define('WP_2_SITEURL', 'http://secondary.example.local');

This post is the result of a question that I originally asked on StackOverflow – Override WP_SITEURL and WP_HOME for WordPress Multisite – and ultimately answered with the help of Chris Murphy.