I'm sure Jerseyparts or one of the other dealer/members of TT can answer specifically, but I believe you have the correct info: Nissan has to prove any mod is THE cause of the failure. Otherwise, they have to cover it.
The short answer is no. Can they void it?...sure...do they?, I've never heard of a CAI doing so. My advice to anyone with a CAI and oiled cone filter?....invest in a can of "CDC MASS AIRFLOW SENSOR CLEANER". and use it at every oil change. It keeps the sensor clean and avoids sensor failure due to a dirty sensor. It will keep you over-oilers out of the crapper.
I just point-blank asked my service manager at the dealer I go to for service. I was told that the Nissmo, Fram Boost and the K&N had the blessings of the service gods.
Keep in mind that was one dealer's approval.
Like Sudden Urge said, keep the stock intake "just in case".
Just keep your Original and change them out if something happens, they will never know. S&B and the Brute Force are the ones that I am looking at, they seem to have the best responses from people and produce the best results.