Customizing error messages

Is there any way to customize the error messages that show up under the submit button? For example, when a user enters an email address that is already in my Mailchimp list, the message: “[email address] is already subscribed to list [list name]. Click here to update your profile.” I would like to edit that message and the others that show, if possible.

Great plugin, by the way 🙂 — just hoping I can make these edits!

http://wordpress.org/plugins/nmedia-mailchimp-widget/