Once a Yahoo ID has been created, it's impossible to change it. However, Yahoo offers options for those unhappy with their current Yahoo ID. Yahoo users can choose to create an additional email address with the same account as an alias or create a new account.
An extra email address can be created for an already existing Yahoo account. Both email addresses merge to the same inbox, and a user can choose which address to use to reply or send email. An alias is an extension of an account created to mask a user's original Yahoo ID and keep it private.