If you are still looking for a way to do this, you can do it with Localization. See how to do localization at http://docs.woothemes.com/document/woocommerce-localization/
In my case, I wanted to change all variations of the word "ship" to the equivalent variation of "deliver" throughout the plugin, both frontend and backend. I'm based in the U.S., and so is my client and all of their customers, so I used the CodeStyling Localization plugin described in the link to create an English/United States localization file for the WooCommerce plugin and made the substitutions there. Since that is the default locale for my client's website, all the translations were done without having to change the base locale (which can be done in wp-config.php if necessary) and without having to change or override any of the WooCommerce code files.
If you want me to send you the resulting localization files, let me know.