I want to download 500 photos to my computer, using Download Originals command in photos. I will then do something with these photos, and then I no longer want them to be downloaded in full resolution to my desktop. I want them to reoptimize and put back in the cloud. How do I do that?
You cannot control which photos will get optimized. It is fully automatic.
Just enable "Optimize Mac Storage" on your Mac for Photos > iCloud again, and Photos will sooner or later remove the downloaded originals from your Mac and replace them by optimized versions on your Mac, but only, if you are low on storage. You cannot force the optimization.
As lang as iCloud Photos is enabled for Photos on your Mac, the photos will always be kept in iCloud, even if "Download originals" is enabled. So you do not have to put the originals back in iCloud. They will have remained in iCloud. You just have to wait for the "Optimize Storage" to kick in. If you want to have all photos immediately to be optimized, you can just wait for your adjustments to be synced to iCloud and then simply delete the complete Photos Library (but keep a backup copy on an external drive). Then create a new, empty Photos Library and enable it as your iCloud Photos Library, but optimized. Your library will be fully optimized right from the start.
Optimize certain photos to the cloud.
