Change email address for Log Archive and Audit accounts

It is technically possible, but it is not formally supported. You would need to go through the documented process that you linked to here already, but then you need to update/repair the landing zone to reflect those changed account emails. You may need to do this a couple of times. What it's doing is updating the CloudFormation stack set parameters to align. Anecdotally I've heard that some customers find that some function as they should, others need a repeated update/repair before those changes propagate. I do not have first hand knowledge of making this change myself.

Yes you can change the email addresses associated with your Control Tower accounts, and per document that is one of the type of changes that are updated automatically by Control Tower, but AWS Service Catalog handles changes differently than AWS Control Tower so you may need to update Service Catalog manually as well since the Provisioned Product for vended accounts in Service Catalog will not be automatically updated to match any changes you make to your accounts. If you want your Provisioned Product to be consistent with the actual state of your vended accounts, you'd need to perform an update in Service Catalog.