Re-association of Apple ID

Apps and media from Apple are tied to Apple ID. iCloud storage, iCloud files, iCloud keychain passwords, iCloud storage of Safari links, etc., are all tied to the Apple ID.*

Local files are not tied to the Apple ID, though the Mac erase and install reset will also clear those.

Untangling these cases—once content and associations are increasingly merged—is unfortunately tedious, yes.

I’d back up to external storage, using Time Machine or maybe a disk copy, make a second complete backup, wipe and re-install macOS per the previous transfer, and as part of the setup in the new environment, log into your Apple ID, and migrate in your previous login environment from one of the two previous backups as part of the setup; using Setup Assistant.

If you decide to use Migration Assistant to migrate your content after the initial macOS setup, then when creating the first admin user during setup, use a different name and different short name, do not use the same short name that you want to use as your login later. This collision ends badly.

*Any of your data that’s associated with the iCloud storage for other Apple ID will need manual cleanup. I’m hoping that you did not use a different Apple ID iCloud account here for your own stuff, and just used what was already installed on the Mac, so you won’t need to migrate and resolve the iCloud storage and contents associated with two Apple IDs.

It’s this sequence: What to do before you sell, give away, or trade in your Mac - Apple Support

Otherwise, any downloaded apps and macOS itself and other such will all be tied to the other ID.

The reset sequence does not differ among Mac Pro pedestal and the MacBook Pro laptop systems.

Superbs wrote:

Thank you for your kind and succinct explanations, suggestions and warnings. I will be careful. I wish Apple made this process safe, secure and simple.

There’s simply no good means to split up the contents of an Apple ID.

As for the Mac, Apple recommends starting over. That’s gotten easier with newer Macs, too.

That’s this: What to do before you sell, give away, or trade in your Mac - Apple Support

But with your own data, where two or more users are sharing the same Apple ID, there’s no automated means to determine the association of people and data, as the mechanism to separate that is the Apple ID.

Again, I’m hoping you didn’t actually share an Apple ID here, and “merely” have an install of macOS and apps associated with a different Apple ID. That’s easier to clean up.

Logout of your Apple ID via system settings> Apple ID

Log back in again with your own Apple ID

WheelieNick wrote:

Logout of your Apple ID via system settings> Apple ID

Log back in again with your own Apple ID

That won’t help with installed apps and updates, unfortunately.