If you modify the suspension then you become responsible for failures caused by the modified suspension.
If the failure is caused by something else then it's only fair that Nissan come to the party. They WILL examine things and see if there's something that has been done that caused the problem - that's sensible on their part. But if your steering wheel cruise control switches fail then they can't blame the winch, or the lift, or the 3" exhaust or even the ChipIt chip - and they won't.
The entire car's warranty is NOT void just because you changed one part of it.