We think we had done this for you earlier using hook. If you have changed the theme or our plugin, then look for the previous one. The hook available which you can use is:
apply_filters( 'wti_like_post_load_message', $msg, $post_id, $like_count, $unlike_count )
You need to attach a function to the above hook. There you need to check for the like, unlike count. Depending upon those values you will have return the message.