From a technical point of view there is a difference between the memo key and the other Authority Roles. The memo key is just a key, while other Authority Roles can have multiple keys and/or authorized accounts assigned to them.

Nevertheless I decided to add also a form for editing the memo key in the tool soon, because it makes sense to change the memo key back to the old one after changing the Master Password to still be able to read old encrypted memos.

Or you can sent this also with the active key?

I'm not sure how exactly the exchanges handle it, if the memo cannot be decrypted with the memo key. Of course, they could try the active key in such a case. If it's not stated on the exchange's website that the active key can be used, I would not try this though :)