Mailing sent with wrong link
Yes. 

There is a way that doesn't involve nginx regex's (https://xkcd.com/208/)

If you are comfortable accessing your civicrm database directly you can locate the correct row in the civicrm_mailing_trackable_url and update the value of the url.

If you run 



select id, url, mailing_id from civicrm_mailing_trackable_url where mailing_id = X;


Where X is the mailing id - you will get a list of urls for that mailing and you should be able to pick out the broken link and update it.