Setting the 'warranty' issue aside, what about the CGA? If the item failed in the above scenario, can we see the CGA not covering it?
As a comparison, in the case of someone making up their own computer, I have never seen such a warranty limitation and there certainly is scope for a non 'professional' to cock things up. If the faulty component was not clearly damaged by the installer, the reseller always honours the warranty in my experience.
Something for the bush lawyers to go at!!
(I did try to google an answer but it doesn't come up specifically enough to settle it).