My wife shattered the screen on her 6s plus last Night. I took it to the 5th Ave store in Manhattan. While waiting for the appointment I backed it up in anticipation of a new phone. The genius took it, looked at it, told me the standard "if the chassis is damaged and the screen doesn't fit you get a new phone" bit. I asked him for a new phone instead of a new screen, to which he told me that "Apple takes the least expensive approach, screen replacement is first". Now I know that different geniuses follow different rules - but this was my experience. This was also the first time I had a somewhat rude genius, maybe because it was late or he was having a bad day, but he was pretty snippy. The only reason I wanted replacement was so that I didn't have to sit and wait for them to fix it, especially since they took me in 30 minutes after the appointment (it was 11:45 at that time). The whole process finished at 2am and on top of that, this morning the ear piece is not working, my wife can hear people only when she uses the speakerphone, which means I have to go back to the store.
So YMMV when taking a phone in.
As crazy as it sounds, I was thinking of driving over it with my car before giving it to the genius, just so they replace it, but that is so wasteful.