CX took it cos they were desperate for some 777s and didnt want to wait. I think they needed to boost capacity for some routes. Boeing refitted and modified the entire aircraft to take the RR Engines instead of the PW ones.
I just flew 4 days ago on a CX777 from HKG to DXB and the captain told me the aircraft was around 5 years old. I didn't get the reg. number, but is it possible I was on the first ever built 777? I really wish I had checked the registration!
To say the #1 Boeing 777 used as a test aircraft was "not in really good shape" is incorrect. 777 #1 had virtually no time on the airframe and was an astute purchase by CX of a pampered low time aircraft. The aircraft was modified to take the RR Trents at the factory, as well as to configure the interior to CX specifications. If my understanding of your comment is incorrect, I apologize.