Sorry guys, maybe I am too dumb today, but you have lost me!
I still believe that somms' initial reply was correct, whereas Element's one and his further elaborations were unfounded.
Of course, we should distinguish between: (1) The legal meaning of Dell's warranty statements, and (2) How Dell handles replacements in practice.
From the legal point of view, I think it is normal that if Dell provides a motherboard for swapping, it takes on the original warranty period (or a bit longer; see below).
As for Atomic Flip's question, if a Dell tech installs anything, it won't void your system warranty, whereas for the processor itself, the following should apply:
"Other add-on hardware carries the longer of either a 1-year limited warranty for new parts and a 90-day limited warranty for reconditioned parts or, for both new and reconditioned parts, the remainder of the warranty for the Dell computer on which such parts are installed."
I don't know what Wooster's comment means.