You can misuse them as such (I've done it myself, albeit on Windows), but they're not really made-to-measure for that use case. E.g. deleting files that have been "tagged" that way becomes more cumbersome (because to the OS all hardlinks are created equal, so deleting the "primary" file doesn't automatically delete the tags, too), it's incompatible with any program that uses "atomic" files saves instead of modifying files in-place, the UI for viewing and editing "tags" is not really there, …