在SE中编写问题时，我已经找到了解决方案：

add_filter( \'get_the_excerpt\', \'get_custom_the_excerpt\' );

function get_custom_the_excerpt($excerpt) {

    $post = get_post();
    $format = get_post_format( $post );

    // modify excerpt if it is a quote, for example set title as author 
    if ($format == \'quote\') {
        $output = \'<q>\'. $excerpt. \'</q>
                <p class="quoted">\'.get_the_title().\'</p>\';
    } 

    // return excerpt without change
    else {
        $output = $excerpt;
    }

    return $output;

}