I went back to »att.yahoo.com/myaccount
and searched all around.
When logged into the particular secondary account, I see no way to rename the account.
Logged into the main email account, I can go to "manage sub accounts". There I can edit or disable a sub account. Disable makes a email to an associated disposable address bounce.
I can create an email alias for the sub account, but I feel confident that the original email address would still be valid.
But I still see no way to rename an account. I don't even see way to delete an account. I was going to try deleting and see if I could recreate the associated disposable email address root on a different secondary account.
Thanks for the suggestion. I would like to think I have just missed
clicking the right thing, but I don't think so. I think this needs
higher level action if it is achievable at all.