Feed Template Customize is a plugin by wokamoto modifies RSS feeds and ATOM feeds as you want.
The plugin provides templates that you put into the current theme folder, then you can use the customized feed templates instead of the default ones.
feed-atom.php – Atom Feed Template for displaying Atom Posts feed.
feed-atom-comments.php – Atom Feed Template for displaying Atom Comments feed.
feed-rdf.php – RSS 1 RDF Feed Template for displaying RSS 1 Posts feed.
feed-rss.php – RSS 0.92 Feed Template for displaying RSS 0.92 Posts feed.
feed-rss2.php – RSS2 Feed Template for displaying RSS2 Posts feed.
feed-rss2-comments.php – RSS2 Feed Template for displaying RSS2 Comments feed.
Download and info: http://wordpress.org/extend/plugins/feed-template-customize/
