ok so if i have removed the original heatsink on my q6600 just to replace the thermal paste does that void the warranty?

What computer is it? It wont void the warranty on the processor it self, but it could void a warrenty depending on who made the computer. It really depends on who built it and if you removed a 'warranty void if broken' sticker.

It's a custom computer, i bought the processor by itself but i don't have the receipt and the box. But i have the invoice from newegg does that count? Also will replacing the stock heatsink with a better heatsink void the warranty? I don't think there's a sticker on the processor, it's just that i thought if the original thermal paste is messed with they will void your warranty.

for custom computers, no. the only time something becomes void is when the actual hardware is messed with. youre just messing about between the hardware