Delayed email -- change of email address?

We are running a longitudinal study that involves email triggers that delay. Specifically, once participants complete Survey A, the workflow add them to the contact list and sends invitations to the next surveys at one week intervals (e.g., Survey B invite goes out after 1 week. Survey C invite goes out after 2 weeks; etc. (up to Survey J)). It runs fine. 

However, if a participant wants to change their email address in the middle (e.g., after Survey D, but before Survey E) is it too late to change it. My understanding is that the emails are all sent when initially triggered (completion of Survey A) but with the assigned delays. Is that correct? I know I can change the email in the contact list, but that won’t change the already sent email invitations, right? 

Is there a way to fix this? Or do we just have to tell that participant that they cannot continue with a different email? Also, they can’t just set up an email rule to forward from the old to the new email because they are closing the old one (because it was expensive(?)).