Is it posible to decrease the score.
I have ~500 Songs with >95.

I would like to decrease every score every day.

is it possible to include this function or can i do it with an externel script (by cron)?

every day: score-1

update statistics set percentage = (percentage + 1) where date(from_unixtime(accessdate)) < subdate(curdate(), 1);

Might help you a little. Wrap it in a script and let it your DB.

(percentage - 1) of course