Actually it's a little more complicated than that. Nissans lifetime (or at least, ~100K) change interval is really only applicable if you drive the car like a grandma and never heat up the fluid much (which might be true of most 7AT's ever sold, so their recommendation does make sense on average).
If you drive the car hard at all, even on the street, you should at least swap the fluid every 20-30K miles or so. Mine was pretty nasty and burnt looking after 20k of mostly-street miles with only a few track weekends. Basically the hotter you get the fluid, the more often it needs changing. Unfortunately we don't get a fluid temp gauge with this car (much less one that tracks peaks, which is what really matters), so unless you install an aftermarket one, you're gonna have to guess, or drain a tiny bit of the fluid and check it's quality (is it really dark? does it smell burnt? does it feel like the same viscosity in your finger as new fluid?). Running a trans fluid cooler can extend the life of it too.
Or you can just do every 20-30K miles for harder street driving and figure you're probably in the ballpark. It's not like the cost of a trans fluid swap on that long of an interval adds much $/mile in the end.
There's a chart of peak temp vs recommended change interval at the end of this PDF (from GTM's instructions for their 7AT upgrades):
http://www.gtmotorsports.com/Manuals..._Procedure.pdf If you do have a temp gauge installed or can estimate your peaks based on IR thermo to the trans pan straight after a hard session, you could roughly go by that.
If you decide to have a dealership swap the fluid for you, be sure to read up on the procedure in the Service Manual (available in the appropriate subform here) yourself, and talk to the service guy at the dealership and make sure that he knows how to do it and that you know how it should be done. Don't let them wing it and hook up some "trans flush" machine like a crappy oil change place does for some random soccer mom SUV. They need to manually drain and fill a portion of the fluid in multiple stages and use Consult-III to monitor fluid temp for proper level setting at the end.