Yeah I figure they wouldn't like it for warranty purposes. I've had it for almost two years though.
Though, I'm not sure how comfortable I feel doing this with such an expensive card lol.
It seems like you can't use the same thermal paste as the one for CPU? I heard it's a thicker paste than the normal CPU stuff.
For the record, if that even matters, I took the GPU out to clean the dust off it and the fans as much as I could.