Always use heat. Hair dryer on low or medium is perfect when removing stickers. Phones are kept together using stick on adhesives including all apple ipads are held together with adhesive. We always used heat and 99% alcohol to take apart. At my work, we have access to manual and automatic pullers with heat and timer that allowed device to get hot in 5 minutes then pull motor starts, that pulls off phone glass back and sometimes screen.
Any liquid will ruin the sticker regardless including adhesive.
Anything hotter than 125C to 150C will melt plastic. Even at 70C you don't want to spend long time heating especially LCD, not the OLED (immune), no more than 10 minutes at a time heating, due to LCD backlight plastic sheets wrinkling ruins the quality of image.
Cheers,
Great Northern aka Canada.