How can I change my email login for iCloud

Please click on the links and read the documents -->

Change your Apple ID - https://support.apple.com/HT202667 - "Follow these steps to change the email address that you use as your Apple ID." Plus special instructions if you want to change your Apple ID to an @icloud.com address. You may also wish to turn off "Find My" before changing information and turn it on again afterward.

"If you try to change your Apple ID to an @icloud.com email address that was created within the last 30 days, you will be asked to try again later.

If you see a message that the email address you want to use isn't available or is already in use, check that you or a family member aren't already using that email address with a different Apple ID. If a family member is using that email address, remove it from their account then try to use it."

I would avoid using an iCloud email address as your Apple ID because should there be problems logging into your account you run the risk of not being able to read the recovery emails from Apple required to fix the problem.

"After you change your Apple ID email address or password, you might need to update your sign-in information with any Apple services you're using" Click on this link to read "What to do after [or before] you change your Apple ID email address or password" --> https://support.apple.com/HT204071

- This is particularly important to do if you use the "Find My" feature. Disable Find My before changing your information, change the information, then reactivate it with the new information.

As you mentioned in the post -

I would avoid using an iCloud email address as your Apple ID because should there be problems logging into your account you run the risk of not being able to read the recovery emails from Apple required to fix the problem.

When web mail address say example1@gmail.com and its password is same as Apple ID and password and signed in Mac system preferences , the mail application is synced with respective accounts ( iCloud as well as gmail ) and applications are turned as on ( specially mail box ) .

If Apple ID is changed from appleid.apple.com it doesn't effect the mail recovery of iCloud or gmail they stay on server and will sync , in case if iPhone / iPad are signed in with same Apple ID and password on the same network it has to be updated the article posted what to do after changing Apple ID or password is to be followed .

Users have different mail accounts in Mac , they can sign out existing Apple ID say example1@gmail.com and sign in with example2@icloud.com from Mac system preferences .

if mail address is used to login iCloud with password with accounts credentials , and used as an Apple ID and signed in Mac / iPhone / iPad see the article Change your Apple ID - Apple Support