Milan Dinić

Change Core Slugs is a plugin that allows you to set custom permalink slugs instead of default ones that are provided with WordPress core. This functionality is already available in WordPress, however it can be used by manually setting new configuration in the code. What this plugin does is that it provides friendly user interface where all site admins can change default slugs.
You can change:
<ul>
<li><code>author</code> base in authors archives</li>
<li><code>search</code> base in searches archives</li>
<li><code>page</code> base in pagination pages of archives or in single posts</li>
<li><code>comments-page</code> base in pagination pages of single posts comments</li>
<li><code>comments</code> base in comments feeds</li>
<li><code>feed</code> base in feeds</li>
</ul>
When you change any slug, you will not get redirection from the pages that used old slug. Same goes if you again change any slug. If you want redirection, you must set it through server rules or with other plugins.
If you disable this plugin, old, default slugs will be restored and URLs with new slugs will stop working. The only way to keep new slugs is by manually setting them in the code.
NOTE: because of two bugs in WordPress core, in some cases setting custom slugs will not work properly. These cases are when <code>page</code> or <code>comments-page</code> include any non-ASCII character (ticket <a href="https://core.trac.wordpress.org/ticket/41891" rel="nofollow ugc">#41891</a>), or when <code>feed</code> or <code>comments</code> bases are set (ticket <a href="https://core.trac.wordpress.org/ticket/43274" rel="nofollow ugc">#43274</a>). Until these two bugs are fixed, you can use <a href="https://github.com/dimadin/redirect-canonical-fix" rel="nofollow ugc">temporary plugin</a> that includes fixes. You do not need that plugin if you do not use features that trigger bugs from above.
And it’s on <a href="https://github.com/dimadin/change-core-slugs" rel="nofollow ugc">GitHub</a>.
<h3>Usage</h3>
Got to Settings > Change Core Slugs page.

Change Core Slugs

Set custom permalink slugs instead of default ones.

Konstantin Obenland

This plugin replaces the author slug with a sanitized version of the user’s display name.
This plugin will not prevent hackers from finding out your login name but the login name won’t be visible 
in the author archive’s URL, which works towards your friendly URLs with using your display name.
DO NOT use this on a site with more than 1000 registered users, as updating all of their nicenames at once might break your site.

WP Author Slug

Easy way to add some obscurity to login guessing.

But please update as it's over 2 years now.

Excellent

This plugin would probably work OK if you have a small number of users (e.g. if your site doesn't allow public login). But if you have a large number of users (e.g. if you are running ecommerce or allow users to register for other reasons), this plugin will probably take down your site.

The reason is that there are hooks that run when you activate or delete the plugin. It runs database fetch and update queries on every user in your database, all in-line on the request (rather than background via a cron). So if you have a thousand or more users it attempts to do a thousand or more database writes when you click Activate or Delete from the plugins list. This will likely grind your website to a halt. 

It would be better/useable if you could either choose to only apply these scripts to specific user types (e.g. Author) or if you could run the update in batches in the background.

Don't use if you have a large user database

Add a layer of security and prevent your login name from being shown in the author archive's URL.

Change Core Slugs vs WP Author Slug