I'm sure this was meant as a "theoretical". Let's avoid discussing specific search terms - that is the policy in our Forum Charter [webmasterworld.com].
One grand overhaul is not the same as frequent changes. Especially because you mention keeping many urls the same, and using 301 redirects when needed, you should be able to pull this off. I would recommend having a Webmaster Tools account so you can send communication to Google if something does go wrong. Also, develop within a test environment and find all the bugs you can before going live. Check our Hot Topics area [webmasterworld.com] for common problems to avoid. It's is always pinned to the top of this forum's index page.