Here is the solution

Go to the file "News\action.default.php" on line 29 and change this:
Now, go to your page and call the RSS Module with your new imageif (isset($params["makerssbutton"]))
{
$image_path = ($params["image"]==null?"images/cms/xml_rss.gif":$params["image"]);
$params["showtemplate"] = "false";
echo $this->CreateLink($id, 'rss', $returnid, "", $params,'',false,false,'',true,'news/rss');
return;
}
Example here{cms_module module='news' category='news*' number="10" makerssbutton="true" image="rss_news.gif"}

www.cvk.fr
Hope this will help you !!
Alex