Hold up! I was wrong. It can't be done. I just tried it every which way, and though you can have an MS account with the same name as your local account, when you try to sign out and sign in using the other account you won't be allowed to. You'll be forced to change the name on one of the accounts first. You can't have a family & other people account with the same name as either your local or MS account either. When you try to sign out and sign in with that other account you'll get the same message telling you that you can't do that. I thought by changing account names to match, and even being able to create new accounts with the same names as other accounts that it would somehow work. Since that in itself doesn't always cause a problem. Sometimes it does though, and it won't even let you do that. But if you try it another way you sometimes can. Which is why when that worked for me I thought that was the end of the story. WRONG! Even if you can get account names to match up...they get you when you try to sign out and sign in using another account. You're forced to choose which name you want to sign back in with. If it matches the one you're trying to sign out with...not happening. So...still yes, technically, you can have a local account with the same name as your MS account. But it's of no practical use to have it that way(since you won't be able to use one of them). Same thing goes for other user accounts, same name yes...it's possible. But you can't sign out from either your local account or your MS account to sign in with another user account if it matches the name of either one.
Anyway, what else I learned besides all that was how your MS account name is set. And it has nothing to do with the email address that you used for the account. It's the first and last name that you gave MS when you signed up for the account. Which you can enter as whatever you want, and change whenever you want. First name "Mr." last name "Genius" is fine. I tried changing mine to that and it worked. There's 2 ways you can change it. You can sign in to Windows using your MS account and go to Settings > Accounts > Your info > Manage my Microsoft account, which will take you to a web page with your account profile where you can edit your name. Or you can go to
https://account.microsoft.com/account/ and sign in with Microsoft to get to the same page. Just don't try changing your name there to match your local account name, or any other user account name...wait...I already said that.