Pardon my asking but not fluent in HG by any means so this inquiry made with that predication accepted.
Are there any non-HG guidelines for non-military vessels to mount torpedo launchers or 'adapt' HG weapon systems to said ships ?
The best example I might give is shown in the film, Soldier of Fortune (1955), Chinese junk owner Clark Gable has a 20mm cannon mounted in the ship's lower deck giving his little ship a string to discourage pursuers.
Another film reference might be the deck-mounted torp launchers on the fastboat as seen in Deep Rising (1998), turning the agile vessel into a very toothy gunboat.
Again, accepted and understood no merchant or privately owned starship can stand toe to toe and slug it out with a dedicated naval (HG) craft but defending against pirates or other small scale engagements might warrant such armament.