I don't think it is, and I'll tell you why. If you already have two Microsoft Accounts, and I mean "on the Microsoft website" accounts, one using ABC@outlook.com and the other using XYZ@outlook.com and both as primary logins you cannot set either address as an alias in the other, for obvious reasons. You can't have one account using the address for another account as its alias. You can use as many e-mail addresses not used either as a primary account alias or a secondary through nth-ary aliases for any other accounts.
I have two Microsoft Accounts using two Gmail addresses, and I have both of those accounts linked to their "mirror Windows 10 user accounts" on my local machine. If I try to go in to the Microsoft Account using the procedure outlined, when I enter the e-mail address of the other as an alias I get a message back saying, "This email address is taken, please try another."
What it sounds like will be necessary is one of two things. One could convert the Windows 10 User Account that exists under ABC@outlook.com to a local account, then convert it back to a Microsoft Account linked account but use the XYZ@outlook.com as the Microsoft Account to link to. To me this is the messier of the two options.
The other would be to create a second Windows 10 user account that's linked to the second Microsoft Account which uses XYZ@outlook.com as it's Microsoft login id. Copy over any user files wanted from the existing Windows 10 user account that already exists and is linked to Microsoft Account ABC@outlook.com. Remove Windows 10 user account that is linked to Microsoft Account ABC@outlook.com, leaving only the account on the machine that is linked to XYZ@outlook.com.
Either way should work.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
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