Hey, I know this answer comes very late xD, but I have some answers to ur questions.

It's not allowed to run the speedrun on a already existing gamefile.

However, through a update there is a new way to navigate between levels. So accidentally 100%ing a level wont affect ur run.

Maybe you still consider running the game and this answer helps!!

I hope to see u soon on the leaderboard!

Hey, is there a possibility to do the speedrun on the Nintendo Switch??