WordPress.org

If you want to enable this feature on all blogs on your MU site:

1. Place the unfiltered-mu.php file in your wp-content/mu-plugins/ directory. That's it. Removing the plugin will remove the capability.

If you want to enable this feature on a blog-by-blog basis:

1. Place the unfiltered-mu.php file in your wp-content/plugins/ directory.
2. Activate this plugin for those blogs on which you want this feature enabled. Deactivating the plugin will remove the capablitiy for that blog.