Can an RSS item be altered with a hook?

the_content_feed is the hook I needed. In my case I am running a regex to replace relative URLs to absolute ones, so I added the following code to functions.php

add_action('the_content_feed', 'relative_to_absolute_links');
function relative_to_absolute_links($content) {
    return preg_replace("/(src=['\"]){1}\/{1}([^\/][^'\"]+)(['\"])/im", "$1" . get_site_url() . "/$2$3", $content);
}