[kellyj00]

my '04 Mustang had the ability to accept a new transponder if you had two keys for it. This wasn't an easy piece of information to find, but it would save you from having to go to the dealer if the nissan works the same way.

Something like turning the car to key "on" twice then back to "acc" for 3 seconds, then turn to off and remove the key, do again with another key that has a valid transponder.... then insert the new key you want to program. This was the ford procedure, I'd imagine nissan has the same type of thing as you can add remotes.