WordPress 3.0 comes with a new filter that lets us customize what is used for each permalink structure tag, other than WordPress default.
One of these permalink structure tags is <code>%category%</code>. By default, WordPress always use the category with lowest ID, making <code>%category%</code> impractical for SEO optimization.
Hikari Category Permalink allows post authors to choose among each post’s categories, which of them is used in that post permalink, giving much more flexibility and power to permalinks.
This plugin is a fork of <a href="https://wordpress.org/extend/plugins/scategory-permalink/" rel="ugc">Dmytro’s sCategory Permalink</a>. It has all original features and is compatible with original options, while being more stable and simple, and also fixes 2 recurring bugs.
<h4>Features</h4>
<ul>
<li>You can choose for each post separately, which category is used in its <code>%category%</code> permalink.</li>
<li>Posts without a category set to be used in permalink behave as WordPress default, (which currently is) the one with lowest ID is used</li>
<li>Posts with a category set have it used</li>
<li>In post edit page, where you set the post’s categories, there’s a new feature allowing you to choose which category will be used in permalink</li>
<li>No rewrite rules tweaks are done, making the plugin much simpler and bug free</li>
<li>If you already used sCategory Permalink, you can safely deactivate it and replace by Hikari Category Permalink, all your category permalinks will be used</li>
</ul>

Hikari Category Permalink

For each post, author can choose which category is used in permalink.

Svetoslav Marinov

orbisius

If you have an existing website and you want to add category to your blog posts links (e.g. by using: /%category%/%postname%/ in Settings > Permalinks) then your visitors 
will most likely run into page not found errors. This plugin checks for such post links and redirects the visitor using permanent (301) redirect to the correct /Category/Permalink link IF the permalinks are setup.
This plugin assumes that you have previously used /%postname%/ in your Settings > Permalinks.
Demo 
http://www.youtube.com/watch?v=L124jV5joTk
Bugs? Suggestions? If you want a faster reponse contact us through our website’s contact form [ orbisius.com ] and not through the support tab of this plugin or WordPress forums. 
We don’t get notified when such requests get posted in the forums.
<a href="http://orbisius.com/go/intro2site?permalinks-to-categorypermalinks" rel="nofollow ugc">Free e-book: How to Build a Website Using WordPress: Beginners Guide</a>
<h4>Author</h4>
Svetoslav Marinov (Slavi) | <a href="http://orbisius.com" title="Custom Web Programming, Web Design, e-commerce, e-store, WordPress Plugin Development, Facebook and Mobile App Development in Niagara Falls, St. Catharines, Ontario, Canada" rel="nofollow ugc">Custom Web and Mobile Programming by Orbisius.com</a>

Permalinks to Category/Permalinks

While it may seem trivial, switching from permalinks to a prefix using a category is tough. Slavi's plugin works just as expected and works out of the box. Definitely recommended.

Works as expected, thanks!

The plugin automatically redirects users who have accessed a blog post link without the category to the one which has the category and therefore avoid …

Hikari Category Permalink vs Permalinks to Category/Permalinks