A tale of woe about iCloud & Apple IDs
TL;DR if your Apple ID email is an icloud.com address don't bother trying to change it to something else, especially if you have an Apple Card associated with it and value your FICO score.
I have an old goofy icloud email address for my Apple ID from many years ago, and wanted to update the address to something new. After reading this article I got some hope that even if I couldn't change my ID to a third-party address that there was at least a means of changing it as long as I could figure out how to make a new iCloud address and associate it with my Apple account as an alias. I was delighted to discover my full first name (it's hyphenated and pretty unique in the world) is available @icloud.com. However when I tried to add that as a "reachable at" address in the Apple ID page, it tried to send a verification as if I'd already created it. You can't create the address without creating a new Apple ID, however, and if you create the ID that address can't be associated with another ID. So how to add the ID as an alias on the account? There's a red herring you can follow, which is to create an email alias in iCloud.com under the email settings. That will let you create an email alias, and even allow you to add it under "reachable at" in the Apple ID page, but still it doesn't show as an option to "Change ID". After deep digging in the forums and discussing with Apple Senior level support they confirmed that once you have a me.com address, the *only* address that counts as an alias is your same address @icloud.com. Period. This feels so inelegant and un-Apple, that you are essentially "punished" by having an Apple email address in that you are stuck with it forever, whereas "non-believers" can switch their Apple ID from gmail to yahoo to hotmail all day if they please.
So I got an idea. Let's bite the bullet, create my new Apple ID, then add that as a "Family Member", migrate all of my content over by signing out, keeping data on the device, signing back in, hitting merge, etc., and have my purchases available through family sharing. I then re-named the old account with the name "Purchase Account" in the family share, and away we go! Thought I was golden! But then, I checked my Wallet in the new ID -- no Apple Card. When I went to add my Apple Card, it started walking me through the Application process fresh. No way, I thought! I've already taken a ding on my credit for the hard inquiry to get this card. I contacted Apple Support, asking them if I could simply swap the card to the new ID, and their answer -- No. I'd need to apply for a new credit card from scratch in order to get my Apple Card associated with the new ID. Totally crushed! So I'm stuck with the dumb old ID. I was even going to go so far as to ditch my old gmail and streamline my life down to two email addresses -- my G Suite for biz and this iCloud for personal. Now instead I've got g suite for biz, gmail for personal, old dumb me.com that is tied to everything and my new cool icloud.com that is pretty much useless except as an email address. First world problems I guess, but still! So inelegant and not Apple-like in the experience.
If you're still reading this -- thanks for hearing my fist shake! Hopefully this saves someone some heartache in the future. 😉