Key-binding signature notation

[Nicolas Le Gland]

Dear list.

I have a perfectly functional key for certification, with an
encryption sub-key and one other for signature. How could I add a
notation to the key-binding signatures?

I could generate a new sub-key, with a key-binding signature notation:

  gpg --cert-notation @key=value --edit-key ######## addkey

But given my existing key and sub-keys, how do I add a new notation?
How can I generate a new key-binding signature with the notation I
want? Likewise, how could I add a preferred keyserver? Or a policy URI
like 0xFFCE1C9A4FADF197 has?

Thank you in advance.

--
Nicolas Le Gland