Board Thread:Questions and Answers/@comment-26044650-20151130173041/@comment-25386610-20160106162200

It just means it will log out of your old account. Your Line account will still be saved (if you have an email on Line). Just that when you log into a new device, the Line on the old device will be logged out.

Edit: You also don't need line to be installed to play Cookie Run. I think that's how others play on 2 devices- by signing on with email on Cookie Run.