Using Child Themes and Modifying Folders within?

It is usually not good practice to edit a theme’s files, as any updates to the theme by the author will likely then override your changes. If you do want to make changes to a theme, then it is best to do it via a child theme.

If you are using a child theme, there is absolutely no reason you should have to edit the parent theme. All your changes can be made via the child theme.

Alternately, if you are simply needing to change some CSS in a theme, you can use Jetpack (http://wordpress.org/plugins/jetpack/) which has a css editor plugin that allows you to make CSS changes without having to modify the theme files or create a child theme.