I think -- a bit in line with what
@Federberg said, that one thing is to evolve and improve shots, and other is to "reinvent" your game. When you improve your backhand -- and/or decide to use it more agressively, you're not reinventing your whole game. Also, I do not see where Nadal "reinvented" his game, at least not in this decade -- he has always been an extremely good tactician and most of the things we see on court were changes he was always able to do mid-match. From his teenage years up to 25, yes, his game evolved quite a bit. The later biggest change would be the serve at 2013 US open.
In other words, to change your tactics against one single player is just that, match tactics. Dimitrov killed Kyrgios with low slices in the Cincy final... smart tactics, but he did not reivented his game.
I would say that Federer started changing his overall strategy back with Annacone. But it was a natural, logical step back then, other steps were taken afterwards, and putting it all together, the move towards more aggression, the new racquet, training, rest, one tweak on the backhand, it all seems like a huge revolution, but it is not. It does not mean it is not
difficult, specially the change of racquets as Murat is stressing.
All in all, Federer was able to reach a new, higher level of play (in comparison to his own self in the last five years to say the least), and
that´s the great accomplishment.
In the "reinvention" category, I guess Nadal and Federer are close, but unlike other aspects, they are both not to high up in this scale. I am quite sure if we had time to pay more attention to lower ranked guys, we could see much bigger transformations (after all, those are the guys who actually need them).