It's not necessarily your warranty that will be voided by the lift - it does depend on what the issue is.
If you try to claim warranty on a component that you have had modified - you are unlikely to get a lot of joy. However, Nissan aren't completely unreasonable - I've used my vehicle off road, but they've covered a few items under warranty. One transfer case seal, one uni joint, one diff seal, steering shaft .. I've had my car lifted 45mm at the front, 85mm at the rear.
If the dealer tries to give you the runaround, just persist (as long as you're right). Example: you've been off-roading, and you've even bottomed the vehicle in a mud pool, and the wiper motor fails. Dealer might try to bullshit you about it, but persist and they'll have to back down. Threatening to call Nissan or the Fair Trading department in your state works wonders when they're being unreasonable.
The greater worry for you is (as they've already pointed out) insurance. Any vehicle can be lifted beyond the rather minimal limits imposed by the motor vehicle authorities as long as they've been certified by an engineer - otherwise the vehicle is technically unroadworthy and that means that the insurer has a technical means of avoiding the policy.