Changes doesn't show up on blog

I am using wordpress in my magento using Fishpig wordpress extension, i have created a functions in functions.php of my theme (though its full integrated, meaning magento theme is applied to blog) but the following function doesn't seem to have any effort. my function is

add_filter( 'the_excerpt_rss', 'insert_thumbnail_into_feed' );
add_filter( 'the_content_feed', 'insert_thumbnail_into_feed' );
function insert_thumbnail_into_feed() {
      global $post;
      if ( has_post_thumbnail( $post-ID ) ){
        // replace thumbnail with yours
        $content = 'p' .get_the_post_thumbnail( $post-ID, 'thumbnail' ) .'/p';
      }

      // get post content and replace feed content with
      // you can also limit/filter the content to exclude shortcodes and html code etc.
      $content .= 'p' .get_the_content() .'/p';

      return $content;
    }

is it because feed by default loads the rss and rss doesn't run the mentioned code? Edit: i am using this Fishpig extension