Board Thread:Help and Questions/@comment-24.146.129.192-20190414151526/@comment-26005122-20190414160403

As long as you're not playing on a child's account, you can transfer you current game data to a LINE acount without losing any progress, aside from scores.

I created a couple of test accounts a while ago to test it out, and I didn't have any issues with losing progress. A long time ago, it was impossible to transfer a guest account to a LINE account. You had to start from scratch, but that's not the case anymore.