Change Author Name to Sitename on Frontend

You could modify it through the the_author filter:

/**
 * Set the author name as the site title.
 */

! is_admin() && add_filter( 'the_author', 
    function( $author )
    {
        return get_bloginfo( 'name' ); 
    }
);

where we change the author name to the site name on the frontend with the help of the get_bloginfo() function.