Renaming Catagories and re-catorgizing products

[size=4][size=4][size=2]I'm wanting to rename and restructured the way my categories and products are listed. My catagories and products are already indexed it Google. I would like to know how this will affect my SEO and will already indexed link go to page not found 404.

I've added cscartrocks CS-Cart Canonical URL and Duplicate Content Fix Addon and I hope this will will redirect all the changed links.

In properly categorizing my products some need to go several subcategories deep. I want to keep my products easy to find with minimal clicks. Any advice and comments on how this will impact potential buyers, site navigation and SEO would be appreciated.[/size][/size][/size]