pork went over internal temperature, can I make it tender by putting the oven in a lower temperature for a couple of hours?
Your pork will not become tender for quite a while. If you plan to shred it, you'll want to aim for about 205 degrees F / 96 degrees C. 

You don't have to go that high if your goal is to slice. 

Either way, a cut like pork shoulder is best cooked low and slow to allow all of the marbled fat to break down. It's an incredibly resilient cut of meat, but it requires patience.

While it is technically "done" as in safe to eat, it's not reached its culinary potential.