I know on the app and computer you can do it multiple times. Not sure about the kiosk but I'd imagine so. One time in particular AS was having an "off" day and my seat assignment kept getting lost and moving me from my upgraded seat in PC to a middle seat at the back of the plane. While on the phone with the agent she had me go in numerous times and check-in to see it what she was doing on her end held up. That is when I learned about this. I'm curious what if any others have experience with multiple check-ins?