Having the option of choosing for every file if we want it in our repository or not would be a great feature. It is currently possible using the wanted expression, but it is not very flexible, or it becomes unmaintainable.

I tried with two repositories a and b, with the following wanted expressions :

* for a: `not metadata=unwanted=<uuid-of-a>`
* for b: `not metadata=unwanted=<uuid-of-b>`

I think those expressions should be included in standard wanted expressions.

Also, to improbe the feature, it should be possible to set (or remove) metadata in directories, and those should automatically affect their content.

And we could imagine a `git annex unwant` command that would add the unwanted metadata to a file, copy it to other repositories, and attempt to drop it.
