If they do however refuse, there's not much you can do to prove otherwise. Unless you can prove you
didn't damage it, they're perfectly within their right to refuse warranty service. And how exactly would you go about proving that you didn't damage it? How could you prove you were properly earthed and didn't cause any ESD damage, or that you didn't mishandle components, or didn't short something out? It's very difficult, if not impossible.
I guess it is, yes. Agreeing and comprehending is 2 totally different things. I don't agree or settle with this, but I can see what it means. I would be very nervous if I'd changed a non-user-upgradable component (that is anything except ram) within a very expensive machine (e.g. nMP). Especially since Apple says they'll consider the warranty as voided.
When the next problem happens, I'd have to convince the official service - somehow - that they should consider the warranty valid. Although I agree as a free-thinking customer with your arguments whether this should void the warranty or not, I think it boils down to that I'd take a big risk to be left without support on such an expensive machine.
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I believe that this sums up everything which could be said in this matter.
Every relevant fact is here clearly exposed. The consequences as well.
Not theory but actual reality if one likes it or not.
If someone wants to take risks, he is free to do it but knowing he is actually taking those risks.
He might be lucky but nobody who thinks and acts in a reasonable way counts on what "might" be when a very expensive piece of equipment is at stake.