No need for a new nip, that is done by the client, but any delete request it's not guaranteed that it is done.
Discussion
You do need a nip for what I'm suggesting. As it stands a kind5 would tell all relays to delete that note. It's not selective.
You just send the delete request to the relays you want and don't send to the one you don't want, but either way, you don't control anything about deletes.
If the ones you don't want still receive the request, (which is likely because clients are supposed to broadcast them when a relay signals they don't have a deletion request when they should) they would delete them when you don't intend for those relays to delete them.
I'm well aware, I made a relay implementation from scratch in go.
Or I can draft up a change to Nip9