[kh99]

If you write a script to do what you described, you can put it in includes/cron and then create a new scheduled task to use it. You can look at the other scripts in that folder to see how they work.

I'm not sure if that's a lot of help - as for the thread pruning, you can find that code in an existing script and copy it. I think admincp/thread.php has code for when you do it from the admincp.