You can change email addresses on an account, but Apple won't let you re-use an email address that has been used with Apple before, not even if you were to delete the account entirely. You will have to come up with a new email address to use with the other account if you wish to change it.
Here's how you change the email address (Apple ID) you use for your Apple Account while retaining everything in your account:
If you have an iPhone or iPad:
1. Go to Settings, then tap your name.
2. Tap Sign In & Security.
3. Next to Email & Phone Numbers, tap Edit.
4. Tap the Remove button next to the email address, then tap Delete.
5. Tap Choose Another Email Address and enter your device passcode if asked.
6. Enter the new email address, then tap Continue.
7. Enter the verification code that was sent to your new email address. Read this support article to learn what to do if you didn’t get the email —> If you didn't receive your verification or reset email - Apple Support
8. If you encounter issues with certain services after doing this, this outdated support article may still have useful suggestions --> What to do after you change your Apple ID or password - Apple Support
Refer to the support article Change your Apple ID - Apple Support :
- If you don’t have an iPhone or iPad the support article says to, “go to https://appleid.apple.com and sign in. Then follow the onscreen instructions to change the email address associated with your Apple ID.”
- For general information, and other issues such as changes or addresses not being accepted.
- Note a recent change to the article where you can now change the email address without having to have access to your old email account.
Although this next section discusses email address re-use in the context of deleting an account, it supports observations frequently posted on this forum about never being able to re-use an email address as an Apple ID once used previously as an Apple ID:
From: How to delete your Apple ID account - Apple Support
"Can I use the primary email address for my deleted Apple ID account to create a new Apple ID or with another existing Apple ID account?
No, once your Apple ID is deleted, you can't use the email address that you used with it to create a new Apple ID. In addition, you can't use that email address with another existing Apple ID except as a rescue [notification] email. Also, if your primary Apple ID email address is with a Custom Email Domain, it can never be reused to create an Apple ID after your Apple ID is deleted, even if the domain ownership changes."
And a related article about using iCloud email aliases - Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support - "Note: You can’t delete or turn off a primary iCloud Mail address. You can’t use an alias to create a separate Apple ID, and an email alias can’t be converted to a primary iCloud Mail address."
