This is impossible as clearly stated on Apple's website:
How to change your Apple ID if it ends with @icloud.com, @me.com or @mac.com
If you use an @icloud.com, @mac.com or @me.com email address as your Apple ID, you can’t change it to a third-party email address.
That is your Apple ID so you can't change it, the only real alternative is to create a ...
It now appears that my wife actually changed my AppleID (although exactly HOW is unclear)
I went to appleid.apple.com/ and have now restored my name, birthday and AppleID
When things settle down I will reset the password to something more sensible.
Presumably to limit account farming, Apple makes it trivial to establish three new accounts on each iOS device or Mac. Since this is detected on Apple’s server side, you can create a new Apple ID from this page (on a desktop computer) or perhaps another device that hasn’t exhausted it’s three.
Once you have set up your new Account, log in on your iPhone ...
The answer to your question is "no". It's not possible to have two computers, both using the same Apple ID, to save files or data to two independent instances of iCloud storage.
However, there may be more to your question. "iCloud" consists of several different features, including iCloud Drive, iCloud Photos, Contacts and Calendar sync, etc. You noted that "...
I think you can only do that (keep separate copies of the files of different computers in the cloud using the same iCloud account) if you sign your computers in with different Apple IDs and use family sharing. In the description of family sharing Apple says
One adult in your household — the organizer — chooses the features your family will share and ...
You can put United States as the country for your Apple ID and, if necessary, use your friend’s US address (or any US address at all) as yours. Apple does not try to verify that you are actually from the US or, by any means, you or someone else is associated with that address. However, Apple will ask for a US-based credit or debit card or a US-based PayPal ...
You can't remove the email functionality from a icloud.com or me.com adress. What you can do instead is to
log into icloud.com in any browser
go to Mail
click on the cog wheel at bottom left and select Settings (first entry in the menu)
set auto-forwarding of all mails to your new email adress
This is a new feature with safari on macOS and Catalina when you are signed in to your iCloud / AppleID on trusted and keychain synchronized devices when communicating to some Apple secure services online.
Your local admin password unlocks they key store and sends a secure token rather than your iCloud password to authenticate you through Safari to Apple’s ...
It is possible to choose which mail to use in Sign in with Apple :
First go to Settings > Your Apple ID > Name, Phone Number, Emails > Make sure the email you want to use is added.
Open the app and click Sign in with Apple and then click on Share my Mail.
It will then propose you which mail associated with you Apple ID you want to use.
Note that it doesn't ...
The user's iTunes ID differs from their Apple ID. It is easy to 'share' your iTunes ID but hard to share your Apple ID.
Your concern is a valid one but for a different reason. No need to be concerned about two different users purchasing two different subscriptions. But you could be concerned that two different users will share their iTunes ID and both ...