As far a s I know you can do anything to the car ie fit nitrous, if your wipers stop working they are still covered as the problem was not caused by the nitrous however if the engine blows up and they can prove it was because of the nitrous you will not be covered. Renault told me that to keep my warranty I had to take it to a Renault Garage for all the services! The conversation went a bit like this:
DO I HAVE TO SERVICE MY CAR AT RENAULT TO KEEP WARRANTY
REPLY YES
BUT DO I HAVE TO
REPLY YES AS WE USE GENUINE PARTS
SO I DONT HAVE TO USE A RENAULT GARAGE THEN
REPLY WE RECOMEND YOU DO
WILL I LOSE MY WARRANTY OR NOT IF I DONT SERVICE MY CAR WITH RENAULT
REPLY, NO YOU WONT AS LONG AS YOU USE GENUINE PARTS!!!!!
SO INSTEAD OF £170 FOR A 12000 MILE SERVICE I PAY £60...BARGAIN.