Except at this point no one has any proof switching hats mid-race and whatever was in them was cheating. This is gray area at most and gray area is still legal.
Personally I love the hat swap. Whether it did nothing more than make Rupp a little more comfortable for a few moments, allow him to take his mind off how f'ing hot he was during the race for a quarter mile, or actually kept his core temperature sightly cooler throughout the race, which tangibly aided in his performance this type of strategizing is part of what makes Salazar and Rupp so impressive to me.
I might have even said the hat swapping could have rattled other athletes during the race, but evidently it did not or there would have been a complaint filed.
I'm really surprised this has not been addressed more so far. The other athletes didn't seem to have any problem with it so why are a bunch of amateurs crying foul?