Galaxy A5: How to set power button to reject calls (no root) I've found in Settings/Answering and ending calls how to answer by pressing Home key and how to end a call by pressing the Power key. Is there any other possibility to assign the power key in order to reject calls? 
Galaxy A5 (2016) Lollipop 5.1.1

Thanks,
No sorry. If you're looking to assign another use to the power button other than what's available in the settings, you'll most likely need to root it.