Effects of changing my Microsoft account's primary alias?

Yes you can change the original email address. This process is called changing the primary alias. The primary alias is the email address that is used to sign in to the account. The article explains how to complete this process.

Hello ChloéThery,

Thank you for posting on the Xbox forums. We understand that you are interested in

changing your primary alias. If you are receiving that error message, it means the email address you want to use is already the primary alias of a Microsoft account. You must first log in to that account. If you need help

resetting the password, you can use our support article. Once you have logged in to that account, you can change the primary alias for it. After you have set up a new primary alias on that account, you can remove the email that you want from it. At that
point, you can go ahead and use that email address as the primary alias of your main account. Be sure to let us know the results!

I changed the email on my gamer tag by signing in to microsoft live account, creating a new alias and assigning it as the primary account, then deleting the old alias.

https://support.xbox.com/en-US/my-account/microsoft-account/change-email-sign-in-for-microsoft-account

You can change the primary email alias on the account

Hello AlanMacielBR,

Thank you for posting on the Xbox forums. We understand that you are interested in learning how you can move an Xbox profile from one Microsoft account to another. At the moment, this feature is not available for Microsoft account. The only option is
to change the primary email address(primary alias) of the Microsoft account that has your Xbox profile. The account owner must

change the primary alias of the account that has your Xbox profile to the intended email address. The account owner can then use the previous email address by adding it as a primary alias to a different Microsoft account. However, If you remove an alias
that's an email address from a Microsoft domain (like @hotmail.com, @live.com, @outlook.com, or @msn.com), you're permanently deleting the alias and it can't be associated with any Microsoft account again. We hope this information helps AlanMacielBR!