How do I exclude individual CSS files from being minified and merged?

You can remove any of your CSS files from being merged or minified by doing the following:

Go to WP-Optimize > Minify > CSS
Scroll to the “Exclude the following CSS files from processing” section
Type in the name of your CSS files — one per line — that you wish to exclude:
Click ‘Save settings’
The files you entered will now be removed from both the minification and merging process and will load as normal.