In shipyard.plist we can set optional and standard equipment, but at the moment there isn't a convenient way to universally forbid a given ship entity having a specific piece of OXP equipment.
I know you can set incompatibilities, and available_to_all as false in the OXP and then only include it in the optional equipment, but that rather relies on you having access to the distributed OXP to add the incompatiblity or the available_to_all flag (I know in my case it's less of a problem than most given my back catalogue that I can tweak as I want, but the comment still applies).
Hence I want to suggest adding a category of "forbidden equipment" or "incompatible equipment" or somesuch to shipdata.plist. That would act much like the above in that any equipment there listed cannot be bought by a player flying that ship (or be installed on NPC ships doing likewise), so equipment could be made incompatible and unavailable from the ship-makers side as well as the OXP side.
Forbidden Equipment
Moderators: winston, another_commander
Forbidden Equipment
My OXPs via Boxspace or from my Wiki pages .
Thargoid TV
Dropbox Referral Link
Thargoid TV
Dropbox Referral Link