Incorrect. The military lowered the P38L's max manifold pressure from factory delivery. Lockheed reps went out to the field to show ground crews to get maximum performance out of their P38Ls.
I don't see how performing a tweak, or removing a restrictor plate, is a field mod. You're comparing apples to oranges. You gonna 'perk your ride' by having a cartoon Lockheed rep come out and pimp your Lightning?