gistfile1.txt

add_filter('template_redirect', 'my_404_override');
add_filter('the_content', 'my_content_override');

function my_404_override()
{
    global $wp_query;

    if (true) {
        status_header(200);
        $wp_query->is_404 = false;
    }
}

function my_content_override()
{
    echo '<div>hello world</div>';
    print_r($_GET);
}