This
"changing to aftermarket cooler will void the warranty" is actually a conspiracy created by the manufactures themselves.
Even among themselves they know such thing should not void the warranty...(infact it could possibly lessen the RMA activity because the aftermarket cooler is better than theirs thus pro-longs the life longevity of the cards.)
See, it's a legal issue thingy, they don't want to be viable by other brand's aftermarket cooler if things goes wrong from the installation of the A.M. cooler...
Just to be on the safe side, the installation of A.M cooler are unfavorable to them and they will rewards us the penalty in the form of 'warranty void' if we were to do so...
So the best thing for any cards owners (everywhere around the world) is to be assertive when changing coolers, LEAVE NO EVIDENCE whatsoever of aftermarket cooler installation when you RMA your cards..
Another thing, when putting back the stock cooler for RMA, remember to tighten the screws the exact "tightness" like how the card came out of the box...if you notice, these screws are pretty tight to screw off first time, some manufacture have a 'certain protocol' of how tight they screw their cards.
When you know this simple rule of 'pandai-pandai tukar heatsink', you can change your coolers multiple times and still be 'RMA eligible'