Kontoname in Windows Mail ändern

I have the same question as this person, whose question, unfortunately, was never answered. How do you change the user name for a Windows Mail account? As already stated, it is grayed out in the account settings, and doesn't appear in the advanced settings either. Why is this not something you can change, while you can edit everything else? Is the only way to change the user name really to delete the account and add it again under a different user name? Only for the new account to appear at the bottom of your email accounts list, of which you cannot change the order?
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