Does migration assistant make any changes to the FROM MAC?

Migration Assistant does not alter the original mac. You can migrate from it again without a problem when you get the new mac.

But don't forget to erase the intermediate mac before you return it!

tanstaafl_42 wrote:

I realized after migration yesterday that I want to return my new Mac and get one with different upgrades. Can I just migrate again from the old computer? Or do I need to do it from the new one (which makes the trade in harder).

Possibly relevant: I am using iCloud Photo Library with A huge collection of photos. Right now, both computers appear to be the system of record, or at least that option is grayed out which usually indicates when is the system of record. The thing I am most concerned about is not losing or duplicating any of my photos.

Yes. Nothing changes on the original source mac or backup.

You have a limited 14 days for a full refund or exchange for one that suits you better.

Call Customer Support (800) MY–APPLE (800–692–7753)

What to do before you sell, give away, or trade in your Mac ...

Use the Setup Assistant on the launch of a new Mac to transfer your user, a pick up where you left off.

The most trouble free way is using the Setup Assistant on the initial boot— you have one shot here.

https://support.apple.com/en-us/HT205749

If that opportunity has past, the second best way is use the Migration Assistant.

How to move your content to a new Mac https://support.apple.com/en-us/HT204350

tanstaafl_42 wrote:

Thank you! And thanks for holding back on any well deserved mockery.

😉.

Good computing tanstaafl_42 !

Same answer as before. None of the methods to bring stuff to a new mac will alter the old one.