Apple ID Account changes?

This is easy.

Use the CHANGE AppleID function described here:

Change your Apple ID - Apple Support

This method will retain all of your apps, purchases, and subscriptions.

See also:

What to do after you've changed your Apple ID or password – Apple Support (AU)

If you use this method, there will be no “old” AppleID to delete.

Note that the “2nd e-Mail” to which you refer is now normally termed the “Notification” eMail; it is most easily set from https://appleid.apple.com/

Which email addresses you use is really a personal preference. The email that I use for my Apple ID is generally my primary personal email, the one I use for most things. The secondary email has changed over time. I often use a work email address but, as jobs change, I need to remember to change it.

Since you asked, this is simply “one person’s opinion” … they may not be practicable by all users, or easily “transitionable” by those with long e-mail histories.

1) Use a non-Apple e-mail provider which YOU control. This allows you to continue to communicate if your AppleID were to somehow become inaccessible to you.

1a) This non-Apple e-mail provider should be VERY secure and reliable; with support for phishing-resistant, crypto-logically based MFA.

1b) The e-mail provider should provide for multiple aliases.

1c) Keep your “actual” email account address closely-held; known only to you and your e-mail provider. Use aliases for everything else.

2) Keep the eMail alias used for your AppleID “out of general circulation” … using it ONLY for your AppleID. This reduces your attack surface exploitable by AppleID scammers.

3) Use other e-mail aliases for day-to-day dealings. Again, if the scamners don’t know your “real” e-mail address, you’re less vulnerable to an account takeover. (it also allows you to more easily “throw-away” an address which has been “leaked”

or become a SPAM-target)

Thanks.

It’s def not for “everybody” …

… but it’s quite “illuminating” to use multiple aliases to more easily determine who is sharing (leaking) your e-mail address with “others” for their own benefit.

I used to know someone, back in the "old days" who would use a different middle initial for every periodical subscription. And I always know if the local electric company has sold my information as they have been spelling my last name wrong in a fairly unusual way for years.

Excellent suggestions!