BisonTech

This plugin replace WP default admin/login/register page. 
The technique used is pretty brutal but the best currently possible, the plugin replaces the modified files automatically. 
To make the plugin run the web server must be able to write to the wp-admin directory. 
more info @ http://www.bisontech.net

LogoReplacer

This plugin replace WP default admin/login/register page.

Christiaan Conover

Relogo lets you easily add support for the rel=”logo” tag to your site. It operates in accordance with the specification published on <a href="http://relogo.org" rel="nofollow ugc">relogo.org</a>.
Using this plugin you can easily add the tag to your site without having to edit any code, and without needing to change your theme’s files. Just provide the URL for your logo’s SVG file, and you’re done.

Relogo

Relogo allows you to easily add support for the rel="logo" spec as described at relogo.org.

LogoReplacer vs Relogo