Hello and welcome to the EVGA forums.
 
If the question is will you loose your warranty if you upgrade the TIM on your GPU the answer is no.
 
Even adding an aftermarket cooler or water block will not effect you warranty. However the original heat sink must need to be replaced in the event a return for replacement becomes necessary.
 
Any time you work on or install components it pays to Be very careful, use a non conductive work surface, wear a anti static wrist strap, handle everything with care, don't force anything and do not to remove any stickers with model # or Serial # on it. When using tools such as needle-nose pliers or screw drivers be gentle so not to damage the PCD or knock off transistor or caps which can happen easily with a slip, because any such damage may be deemed excessive and warranty terminated.
 
EVGA supports enthusiast more so than any other manufacturer IMO and even has an open policy that supports over clocking there products. Common sense is all you need to comply and if ever in doubt, consult fellow users and moderators here on these forums.
 
Again WELCOME!