My question now is - can I swap out the original RAWs stored in the cloud for Smart Previews of those files created in LRClassic in order to save space in the cloud?
If so, how do I do this?
By @robkendrew
Yes you can do that, and it's quite easy. Basically you have to unsync the images in LrClassic, which will cause the originals in the cloud to be deleted. Once deleted, you the resync them from LrC which will upload the Smart Previews to the cloud.
To do that you would need to select all the target images in LrC, then go to the All Synced Photographs special collection while retaining the select status, then right-click on any one of the selected images and click on "Remove from All Synced Photographs". Once that removal has synced to the cloud, you can then either add them back to the All Synced Photographs collection, or (to make them easier to find in the cloud) add them to a new collection (or an existing synced collection) and then enable that collection to sync.
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