Symlinks seem to be more popular - people use them e.g. when moving installed games from one disk to another. I've been using them for years. Tried them with uTorrent a few years ago - and it didn't work, apparently because it's adding ".!ut" to incomplete files, and it breaks the link. Only now I tried hard links - and it works. And with DupeGuru you can even remove duplicates from overlapping packs, but still keep seeding them all, thanks to hard links.

The way you can do this is with hardlinks. They're more or less filesystem-level shortcuts, so you can have multiple "files" with different names and even different file extensions - all pointing to the same file on the disk.

You can add hardlinks with the program called Link Shell Extension. (Symlinks won't work if the torrent client tries renaming the file).

You also can use the program called DupeGuru to automatically look for duplicates and replace them with hardlinks.