If it is like Modern Warfare 3, it is a game update, not a system update. This update is safe to do.

It does require that you have access to Shop Channel. So if you don’t due to your mod (it will ask you to do an update before you can access Shop Channel), then follow this guide: http://www.wiihacks.com/other-faq-gu…21-update.html to get yourself current so you can access the game update.