Working with 301 redirects and links

Hi
I have a few questions regarding how the incoming links to a site and its pages will be affected if I change the permalink structure of my website with and w.out doing 301 redirects.

1. If my current permalink setting is sitename.com/post and I change it to sitename.com/cat/postname, will the incoming links to sitename.com/postname be broken?

2. I did a few directory submissions, which have been devalued by Google (read over at SEL), so will changing my home page from sitename.com/ to sitename.com/home break those links too? I am asking both for: If I manually redirect all pages (and) If I dont manually redirect all/any pages.

P.S- I may or may not be informing sites linking in to change/update the URL.

Thanks in advance ??