Feed templates are special case. You can’t simply provide your own template – you need to work with do_feed_
hooks to change handler function.
But for your specific question it is much easier to override author. Try this (not tested):
add_filter( 'the_author', 'feed_author' );
function feed_author($name) {
if( is_feed() )
return 'Acme, Inc.';
return $name;
}