我结合这两篇帖子的答案，自己想出了如何重新调整附件的标题：

How can I add a default description to uploaded files?

Change attachment filename

function wpse_retitle_attachment( $post_ID )
{
    $file = get_attached_file($post_ID);
    $path = pathinfo($file);
    $args = array( 
                    \'ID\'           => $post_ID, 
                    \'post_title\'   => $path[\'filename\'] . "." . $path[\'extension\'], 
                    // \'post_excerpt\' => \'My default caption ...\', 
                    // \'post_content\' => \'My default description ...\', 
            );

    wp_update_post( $args );

}
add_action( \'add_attachment\', \'wpse_retitle_attachment\' );