How can I remove/change the icloud.com alias on my apple id account There are two email addresses listed in my apple id settings (section "REACHABLE AT"):

me@mydomian.com
my.oldname@icloud.com


The first is my login address. I want to change or remove the second one. How can I do this?
Apple does not let you delete or change the primary iCloud email address. You can stop using it, but it'll always be associated with that account.

See also https://support.apple.com/ht202667, the section titled "If you can't change your Apple ID", which while is not the exact situation you're in, it explains how they look at it.