Leagally the dealer has to prove a mod caused a problem before they can deny warranty coverage. There is a link on the Maxima.org forums about this, but it is down at the moment.

Of course if the dealer wants to deny warranty coverage due to mods it could be a huge PITA that most people would not want to go through. Some dealers are more mod freindly than others, perhaps you shoud ask around before you have a mod installed. It is probably worth paying a little more to have a dealer do it if they will still honer the warranty without a hassel.

98 Maxima SE, 5-speed.