The jdupes deduplication program allows you to create hardlinks, so that the files are not deleted, but linked together so that the disk space is used only once for multiple copies.
Is there a way to control which file of the duplicates is kept? Normally it would not matter, but when using volume or file system snapshots, replacing a file in a snapshot with a link to a new copy only frees space when the snapshot is deleted. Linking the file from the snapshot to the new copy (which is not yet in any snapshot) will free space.
