UPDATE `wp_posts` 
SET post_content = '/mp4/'
WHERE post_content ='http://musicais.ddns.net';

UPDATE wp_posts
SET post_content = '/mp4/' 
WHERE post_content = 'https://www.dropbox.com/';

DELETE FROM wp_post
WHERE post_content = 'https://www.dropbox.com/s/*/';

funcionou assim:
UPDATE wp_posts SET post_content = replace(guid, 'http://musicais.ddns.net/','http://midia.antonini.psc.br/')

UPDATE wp_posts
SET post_status = 'private' 
WHERE post_status = 'publish';

UPDATE wp_posts
SET post_status = 'publish' 
WHERE post_status = 'private';