There are no remotes "programmed" for anyones Xterra, there are Xterras programmed to pay attention to certain remotes. I don't know how many different "patterns" there are for the remotes, probably a few dozen, but obviously not all remotes are unique and you could take your remote to a dealer lot and most likely find another X (or other Nissan for that matter) that will respond to it. There are a lot of people out there with remotes that transmit the exact same "pattern" that yours does too, so you can't really make your X listen only to "your" remote since it is not unique.

You do not have to re-program your X to pay attention to your other remote, it keeps track of up to 4. Hell, it might even be possible that both of your remotes transmit the same "pattern" and it won't matter regardless.

Brent