Even though it's a codeshare, it is still operated by AF, so you can't just nonrev on it like it was a DL flight. I know that AF and DL have a special agreement now, like a half priced ZED, or service charge or something like that that is cheaper than a regular ZED. You still have to buy the ticket very similar to a ZED, and officially it is for travel in Y only.

Totally depends on the individuals working the flight that day. When I was a gate agent, I always put all the nonrevs in F, even if it wasn't in the agreement, because hopefully it comes back around to me at some point. I've heard that the majority of gate agents at AF are pretty strict about Y only. Not sure what happens if Y is full and J is open. EK in SYD moved some Y pax to J to get me on in Y, as they wouldn't put me on in J. Always nicer when Y is full and they just stick you in J.

Good luck with your trip.