Editing feed for thumbnails and link

Question

I want to display post thumbnails and hyperlinks in post on my feed page. I know in templates you can copy page template and modify it, but here i am dealing with wp-includes/feed.php or wp-includes/feed-rss . I have two question

1. what can i do get to get thumbnails of post and links of post?
2. If i edit the feed template, tomorrow when wordpress updates, it will remove my custom code, how can i make it like a child-template, so my code doesn't get disturbed, when new updates come.

Answer 1

you don't need to edit WordPress core files and don't do this, when hooks are available to modify use the_excerpt_rss and the_content_feed filter to add thumbnails or your custom links in feed.

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;
}

EDIT: place this code in your theme's functions.php