You can literally do just about anything from a Child theme.
If you use the custom.css file in the sample theme, it will override. It’s the same as putting it in your “Custom CSS” option. Checkout this video: http://vimeo.com/41331677
This is searchable archive of our old support forums, which operated from 2012 - 2016. To find out how to get support for your current theme, please visit our support page.