Replace the RSS feed icon button "Chicklet" with your own custom icons - Google Blogger Blog - Feedburner

 Interesting link for changing the feedburner icon
http://www.blog.blogbait-blogger.com/2008/10/replace-rss-feed-icon-button-with-your.html
Interesting link for changing the layout of feedburner chicklet
http://labnol.blogspot.com/2006/12/feedburner-tip-change-text-inside.html