You are going to need to overturn the 1958 Convention on the High Seas (Article 15) and the UN Convention on the Law of the Sea (Article 101). They contain the identical wording:
(a) any illegal acts of violence or detention, or any act of depredation, committed for private ends by the crew or the passengers of a private ship or a private aircraft, and directed—
(i) on the high seas, against another ship or aircraft, or against persons or property on board such ship or aircraft;
(ii) against a ship, aircraft, persons or property in a place outside the jurisdiction of any State;
(b) any act of voluntary participation in the operation of a ship or of an aircraft with knowledge of facts making it a pirate ship or aircraft;
(c) any act of inciting or of intentionally facilitating an act described in subparagraph (a) or (b).
They make no distinction between piracy and privateering (something that was always more a matter of whose ox was being gored even when privateers were fairly common).
Even when privateering was a going concern there were serious restraints on the practice. Privateers had to operate beyond what came to be known as "cruiser rules" in the year's leading up to the Great War. Privateers were REQUIRED to provide a safe and secure place for the crew and passengers of any vessel taken, not simply allow them time to get into ship's boats.
Under today's international law privateers would also fall under the heading of mercenaries or soldiers for hire. That puts them outside the protection of the Laws of Wars (the same mainly holds for PMC units, which is why they have to be included in any "Status on Forces" agreements).