As I remember when I called NIRO about this sometime ago, was told WARRANTY not affected by putting Trailer Hitch on vehicle.
Limit would be the load capacity of the car which is rated at like 800 pounds (that includes passengers, inside load, and trailer).
So, how that would work out in a Warranty Situation --- is beyond me. Can't tow hardly anything if you stick to a total 800 pound limit.
Well, sort of... 850lbs is load capacity. That's how much the car can hold up. The amount it can tow horizontally is significantly more. I have had nearly 1200 lbs of people in it before, and it survived.
This car if it was rated would probably be Class A. If you can buy a Class III made for the car, then the car has the ability to go forward with a Class III trailer loaded. If you put a Class I hitch on it, it has pretty much the same down force on the suspension as you sitting on the bumper. If you get into the Class III realm which is 6000#, now you are getting to the area where you will exceed the limits of the brakes on the car. You should never do that, unless the trailer has brakes also.
Tongue Weight is critical when loading a trailer. Class III is rated for 525 lbs, so imagine 500 lbs sitting on your bumper, bad news in this car.
A trailer should be loaded with pretty much all the weight on the trailer axle(s) for a bumper pull trailer, say 52/48 for weight distribution balanced on the axle. Small things like lawn equipment and bedroom furniture is relatively light, and really doesn't matter. But a 6x12 3500 lb trailer with a 1800 lb mower changes the equation a lot.
The niro will have zero issues pulling a 5x8 or a 4x10 or 4x6 or smaller. Anything larger then you need a brake axle on the trailer and a brake controller. Very few trailers with one axle have brakes, but it's not impossible.
I did it and it works perfectly fine. I only go 35 mph when I pull it, and it is still fine. I would never consider pulling more than 2000 lb in this car faster, or at highway speeds. It's not at all impossible, it's just not safe.