On: Japan HP accidentally deleted 77TB data in Kyoto U. supercomputing system

[thaumasiotes]

Well, it looks like creating another hard link is a nearly-free solution. And beyond that, since emacs already has both behaviors, presumably you can tell it you want the in-place modification.

[kragen → thaumasiotes]

I think you can just customize the backup-by-copying variable to t, though I haven't tried it. Check the manual.