I believe once you Opt Out, that follows you even if you move. They attach it to your report and your SSN.
Usually they will want a copy of your Driver's License and SSN card. If your state permits a DL to contain a PO Box, then they might accept it. There are some PO Boxes out there that resemble a street address, but the CRAs probably buy the USPS's products that let them do address verification and determine something is a PO Box.