Whenever you modify a category, a post slug, or the permalink structure in your blog the links on the web (also by search engines) to the old permalinks get broken and therefore you lose visitors traffic and pagerank.
However, there are free plugins dealing with this problem and allowing you to safely change permalinks without losing reference to the previous ones,
Here’s a list of some of the permalink plugins available:
- Dean’s Permalinks Migration by Dean Lee – With this plugin, you can safely change your permalink structure without breaking the old links to your website.
- jadedcoder Sticky Permalinks by Matthew Horner – Every time you modify a post slug, add a new post, rename a category, or otherwise modify any of your post and page permalinks, jadedcoder Sticky Permalinks (jcsp) will keep a copy of the original permalink along with the post or page it originally led to. If anyone tries to access the old URL, they will be redirected right to the new one, no matter how many times you’ve changed it.
- Permalinks Moved Permanently by Microkid – If you just migrated your WordPress blog from one permalink structure to another, right before the old permalink generates a 404 error, this plugin grabs the slug from the end of the request and checks if there is a post with this slug living somewhere else on your blog. If so, it will generate a “301 Moved Permanently” error, which automatically forwards your visitor (and Googlebot) to the new location of your post. No configuration options, just plug and play.
