you only void the warranty on the part you have taken off but with all new parts u get a warranty any way
not necessarily mate, some aftermarket parts may in the dealers eyes cause strain on adjoining standard parts which would in turn void an all component warranty
saying that though as long as your sensible and dont bolt a supercharger on you'll be just fine, eg i have a milly and an evoms cai, 19's and many other bits and my dealer is totally cool with them. its worth remembering that even if your delaer isnt to good about it, depending on what you fit you could always put the stock item back on whenever the car goes back to the dealership, mildly modding is the key