A new aquaintance asked me about changing permalinks. He has a successful blog with lots of posts, and he wants to be sure to keep all the link juice associated with the old URLs for those posts.
His site had a kind of default permalink structure that did not use English language words in the URLs. He wanted to change this so that it would use English words, like Business Blogging 101 does.
There’s a plugin for that called WordPress Redirection.
He also wanted to change his category names, since he had been using only one “general” category for all his posts. Here’s my advice on that point.
I’m not sure of all the implications of changing categories retroactively. I know that it’s possible to simply create new categories and assign them to old posts. You can delete an old category and, if that’s the only one assigned to a post, WordPress will ask which category you want to replace it.
Before going further with any of this, be sure to back up your database and also use Tools > Export to export an .xml file of your site. You should back up files in the wp-content directory regularly as well (although that’s not directly affected by these changes).
Some people choose to exclude categories from Google using noindex to avoid duplicate content issues. IMO, I don’t think you need to worry about this. Google has gotten much better at ignoring duplicate content.
If you are very keen on increasing search optimization using categories, you can remove the “general” cat and replace it with more specific cats on each post. I favor using only one category per post. You can use tags for any other keywords you want to associate with posts.
If you have lots of “general” posts, I would not worry about going back to do this. Leave the general category. Create new, more specific categories, and use those going forward. The most important thing for blog SEO is that you keep producing good content on a consistent basis and get lots of comments from readers like you are doing. That will also lead to more people linking to you. The SEO significance of categories on older posts is not nearly as great as these things.
Lorelle VanFossen is a great WordPress resource, in general, and about categories and tags among other things.