That means you cannot modify the card in any way, shape, or form. That includes the cooler and any unauthorized BIOS update.
The quote you provide seems to be related to things that can happen to your card whether or not it is your fault like water damage from a leaky roof, damage from a sudden surge of electricity (like a lightning strike) and other "acts of god".
Only a few brand names will allow you to mod the video card and not void the warranty; assuming you did not royally mess up the card. XFX and EVGA are on that list.