If you use our Updates & Newsletters service, you can change a buyer's email address for that in Seller Admin under Manage Buyers > View/Edit Email Lists. Note they will be listed in the Buyer Group there for each different item they've purchased, so we'd advise doing a search for their old email, then you can update them all at once.
Aside from that, their original order details in your Transaction Log cannot be edited, as that's a permanent record of their order as originally placed. If you're reactivating their old link(s) and need to resend the link to them, you can simply untick Resend thank-you email(s) to original buyer, copy the link reactivated there, and paste that into a personal email to the buyer's new email address.
