IS it possible to modify a Vapochill cooling system so that a seperate pipe can come off the main pipe going to the cpu, so that it can be used to cool the gpu also ?
Not to my knowledge. Even just taking it apart and reassembling it would probably need an HVAC engineer but even so... the way the Phase Change cycle works would necessitate another compressor, and condensor circuit as well as the second evaporator you're talking about. I don't think you can do it how I think you're visualising it, anyway.
in theory... it has a high pressure tube (very short in diameter) and a low pressure tube (other way around) well. if u make the low pressure tube go to the GPU after going to the cpu as it's cold you could cool down the gpu with the tube that comes from the CPU to the compressor making it pass throu the gpu before the compressor... but im not the expert... only the theory guy LooL
dont think that'll work because vapochills work by phase change, they cooling comes from the cpu heat being used to convert a liquid to a gas which is then condensed and sent back down again