I don't have a problem with it. As long as Superman still looks like Superman, I don't care how much they change the race, sex, or hair color of the supporting characters.
They've always been pretty thinly defined in the comics and movies anyway.
The only problem I have with it is that a potential female Jimmy Olsen already exists in Chloe Sullivan. They could have actually made the movie more, not less, diverse if they'd used Chloe and Jimmy.