No matter how many angels dance on the head of your pin he needs a ferry permit before he can fly it over the heads of the populace due to the presence of damage forcing a change in the major parts.
He needed that official permission before the 'first' flight. And given there are new blades on the engine that were not there when declared airworthy by the FAA, it is now 'untested' until the FAA decides whether to just agree with his sign off or whether to require some hours be flown off as proof..
Yeah, we get the initial sign off and then proceed to make major changes based on our own signature. That works until the day there is an accident/injury and the FAA decides that you pushed it too far and the aircraft was not legally permitted to fly and the brown stuff starts splattering all over the freshly painted white walls...
Now you can sneer and argue with me and quote parts of the FAR all you want (shrug) but I will be an interested spectator when you try that with the FAA attorney assigned to your case. I do like popcorn btw - buttered and lightly salted.