I'm doing a clean install on a new HD for various reasons, and I'd like to move my 700GB Photos library over. I also want the library to continue to sync with iCloud.
Since the existing library is synced, one way would be to create a new empty Photos library in the new system, turn on "iCloud Photos" and let it download the whole set from iCloud. Unfortunately that would take weeks and exhaust my data cap many times over, so I'd like to avoid this if possible.
I don't think I can use Migration Assistant because it will also move over all the stuff I'm doing a clean install to avoid.
I tried copying the system Photos Library, "Photos Library.photoslibrary" to the new HD. The copy went fine, I booted from the new drive and opened it, set it as the system library, and turned on iCloud Photos. It said "Updating" for a minute, then switched to "Uploading 100,000 photos". I paused it immediately and turned off iCloud Photos. I'm assuming this means it would treat all the photos in the copied library as new, and duplicate everything.
So my question is, is there a way to copy my full Photos library and maintain iCloud sync without downloading all 700GB from iCloud?