Lets say the tyres of my new car is Yokohama brand, but if i change to other brands like Michelin, will it void the warranty?
Nope. Unless you change the alloys as well and the size of the rims is out of the safe range written in the manual.
It's highly likely that your car warranty does not cover the tyres.
even you change rims etc, i dont think they cover, they cover the enginee and some parts.. it doesnt cover most kind of physical damage
Okay, let me try to explain a little bit more clearly. It is true warranty don't cover your tyres. They may cover the rims though, if it is stock. If you decide to change to your own aftermarket rims and tyres, it will not void the warranty in most cases.
But there is a possibility you might void the warranty because you change the tyres and rims. It is possible to void the warranty if the rims you are changing to is out of the safe limit as stated in the car's manual. Usually the manual will state what's the biggest rims you can fit. For example: 18-inch, 235mm wide. If you fit anything bigger than 18-inch and 235mm wide, you might void the warranty.
Reason being, when you fit rims that are very very big, you risk adding more stress to the suspension system. So if your car's suspension system has problems and the aftermarket rims you are using is out of the safe limit, they might just void your warranty.
But of course, TS is talking about changing tyres. Let's assume here TS has absolutely no intention of changing away the stock rims. Just changing the tyres from, let's say, Yokohama to Bridgestone won't void the warranty in any way.