Can you be more detailed?
Are talking about the Outlook switch? If that is the case, then the extension has change (@outlook versus @msn or @hotmail) and it is a new email address. If you are trying to change your email, then it can't be the one you used for 20 years ...you are changing it, no?
I think I am missing some information so can you flesh it out?
If you leave your email address as it is, in the case of msn,they will automatically switch it and keep using the msn or hotmail extension. At least for now, nothing much changes.
Thoreau said, 'A man is rich in proportion to the things he can leave alone.'