Changing 'Use as featured image' link text


For use on a classifieds website, I think it would be more clear for the user if the featured image link said ‘set listing image’ rather than ‘set featured image’. I found where the link text from the ‘Add Classified’ page is specified in the plugin’s core.php file; I’m now looking to change the link inside the media uploader to say ‘Use as listing image’ instead of ‘Use as featured image’. I suspect this might be a WordPress core setting but I’m not certain. Any ideas? Thanks