S-D,
sorry, a bit of a terse observation on my part.
As I understood it, the MAA's main issue with the Rivet Joint exercise was the absence of complete traceability of the certification evidence to a known design baseline. Some of the required evidence would have dated back to the original civil certification exercise (Boeing's problem) and some was the DOD's responsibility; the passage of time hadn't helped either party. I was speculating that similar issues could arise with the P8 because of its fairly extended type family history, most of it under Boeing's responsibility. I'd expect the DOD to have no problem as such with the P8 mods.
I'd also wonder whether FMS conditions would help or hinder the UK in obtaining access to the necessary evidence. The C17 is probably a useful precedent but I know nothing about it. What I have observed in the fast jet world suggests there is scope for problems to arise.
EAP