It will not void the warranty unless you screw up and cause something to break.
Worst situation - you will be buying a new heatsink and CPU (if you REALLY fuk up!!

) which is not too bad IMO...
Everything else is grey area...someone will have to actually experience it for the others to know what will happen...and atm it looks like I am first in line because I have completely changed my 5660's cooling system by removing the pads, lapping the heatsink and CPU and using thermal paste)
Think about it and do it only if you think it is gonna be worth it and if you have the requisite skill. For me it was worth it...no more table fan on the side to improve cooling...
But I think just cleaning out your heatsink will have a good result...
