So, as long as you return the key of your PO box when it expires, they won't change the lock.
Before returning it, go to Home Depot and clone it for like $5.
Wait a month or so, and then go into the PO box room at night (beware of bums) to open your old box with clone key. Take note of new owner's name, from mail..
Now you can have whatever "shady goods" delivered to THAT guy, and pick them up yourself at night.
You're welcome.