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With this plugin, you can safely change your permalink structure without breaking the old links to your website, and even doesn’t affect your search engine rankings.

Introduction

Many people want to change their permalink structure, for example, from /%year%/%monthnum%/%day%/%postname%/ to /%category%/%postname%/

But doing so will make all pages indexed by search engines become invalid, moreover, losing visitors from other sites or bookmarks that links to you.

There is a way to tell the search engines (and browsers) that the page has permanently moved, and that the old address should be replaced by the new one. It’s called a “301 Redirect”, also known as a Permanent Redirect. When you do this, Search engines will update their indexes quickly and you won’t lose your page rank. you will continue to receive traffic as though nothing had changed. This works for search engines, bookmarks, and links from other sites.

By now, you know how you can change your permalinks without losing the traffic you’re already getting. You can download this Permalink Migration Plugin to achieve this for you.

This plugin will generates a “301 Redirect” when user or spider visit your site through old permalinks, and redirect them to the new permalinks of the same post.

Do not fear to change your permalink structure now, you would never lose any visitors due to changed addresses.

http://wordpress.org/extend/plugins/permalinks-migration-plugin-for-wordpress/

Installation

1. unzip and upload the file into your wp-content/plugins/ directory.
2. Activate it on your Admin Panel->Plugin Management page.

Usage

1. goto admin panel->options->PermalinksMigration.set the old permanlink structure of your site.
2. goto admin panel->options->Permalinks.change the new permalink structure to what you want. (personally I recommend /%category%/%postname%/, you can read @ArunBasilLal’s tour  to learn more about how to Optimizing Permalinks for Better SEO)
3. Done,enjoy it.

Acknowledgement: http://www.deanlee.cn