Change order status on print packing slip

This should be a pretty simple one, just a little over my head as I am still learning PHP.

Instead of manually changing the order status to “in progress” after printing the packing slip I would like to do it automatically. Yes, there is a chance it may need to be reversed if a problem is found, but that is easy enough to do and saves me the effort 99% of the time.

Basically should be one line of code added to the bottom of the print_packing_slip.tpl that sets the status to “In Progress” and initiates a customer only notification. This code would be exectued when the print packing slip window pops ups.

I have a rough idea of parts of it, but not sure on the exact. Any help would be appreciated.

suffix=“o” id=$o.order_id


items_status=“In Progress”