Just had a meaningful chat with our Nissan TSM about add-on transmission coolers and warranty. I was surprised to hear that a properly-installed accessory cooler will not
void the CVT warranty unless it directly contributes to a failure (leaking, clogging, etc). However, one direct contribution that isn't obvious would be over-cooling, especially for those living in climates with long periods of cold weather. Nissan CVT's don't have fluid thermostats, so even if the beehive and in-radiator cooler are left in place by way of series installation, the trans may not be able to warm itself in brutally cold conditions.
The upshot of this is, part of a proper
installation for warranty purposes will be adding a thermostatic bypass valve. These are also called H-Valves in the industry, and work by recirculating flow back to the transmission until the fluid reaches a preset temperature, then allowing flow to reach the cooler. They use simple shuttle valves that are incredibly simple and reliable. There are two popular ones out there made by Derale and Dana/Tru-Cool, both of which open at 180F and are available for about $50 on eBay or Amazon:
The 180F opening temperature is very near the ideal 176F "sweet spot" for CVT's, so it should work fine for preserving both your CVT and your warranty. I just ordered the Derale version for our Altima, which tends to run around 155F on the highway with a Hayden 512 cooler. It's no longer under warranty, but ideal is ideal. For $50 it seems like a no-brainer.