Does anyone know if there is a way to change a drop shipment purchase order to a special order purchase order without deleting/canceling the order and recreating?

Unfortunately not. However, there is a setting in the company features to unable Item Receipts on Drop Ship purchase orders. I understand this could change many processes for you, so I am not suggesting you switch that on, but it might be the only option if you don't want to delete/cancel the PO.

This is what I figured, but had to ask in case I was missing something.

Just realised I said "unable" but meant "enable" - I think you got the gist of it though.