but there are still plenty of random little things I'd like to hang on to it for.
Changing email addresses is a nightmare, I know. A lot of companies are not event technologically equipped to handle it because, as far as they're concerned, your email address IS your account, and account numbers are not a thing. But you need to bite the bullet and get it done. That sounds like a huge security vulnerability.
It's a Microsoft account, and my windows is tied to it
"tied to it" how? Use a local account. No Microsoft necessary. Alternatively, stop using Windows ๐