Can anyone tell me why this Wordpress Plugin code is not working?

function rss_change($content) {
if(is_feed()) {
return $content . '. Copyrights ©2012 Test.com';
}
return $content;
}

add_filter('the_content', 'rss_change');

I have added the /* comments which is required to activate and deactivate. After activation. RSS is not changing at http:/{site}/wordpress/rss