Hello and Hi. After like 4 years I am again publishing a new plugin for wordpress that allows you to Add Custom messages Text or HTML in your RSS feed.
Here are 2 screenshots for it.
Download it from here : http://wordpress.org/extend/plugins/custom-messages-in-rss-feed/
Direct Download : http://downloads.wordpress.org/plugin/custom-messages-in-rss-feed.zip
Once you have this plugin installed and activated. You can specify almost any text or HTML that you can append or prepend in your RSS feed.
Can be used in many ways. Just depends on your imagination.
Let me know if there are any issues with it. For troubleshooting you can contact me from my contacts page.