you talking about rss_xml.tpl ?
if so, i have modified it many times for my needs on various sites.
example would be to include a thumbnail for certain feeds, kinda like wordpress does for a special topic thumbnail field.
if you could be more specific about what you want there, i'm _sure_ there is a solution.
it might even involve modifying the ubbthreads.inc.php 'generate_rss_feeds' code to supply more smarty variables to the template.
all doable
