You cannot change your mind. Once you appoint a nominee, you cannot change it. Here is exactly what it says on AC website.

"Once you have completed your list of eUpgrade Nominees, you will not be able to change it. However, you will be able to deactivate a nominee if you no longer wish for them to use your eUpgrade Credits, and reactivate them if you change your mind later. Please note that deactivating an eUpgrade Nominee does not enable you to add an additional nominee."

It goes on to say

"As an eUpgrade account owner, you will always be responsible for requesting an upgrade for your eUpgrade Nominees. The eUpgrade Nominees themselves cannot request upgrades using your eUpgrade Credits."

If you no longer wish for someone to use your credits, just don't request any upgrades for them! No need for deactivating. All this does it confuse people. I would love to hear from AC the rationale behind introducing this function.

The only possible usefulness would be if you could use it cancel an upgrade request that you already made. It's not clear if this is the case. What is the procedure for cancelling an confirmed upgrade or a wait listed upgrade? Would the nominee or the sponsor have to make the request?