Can this be adjusted to attach turrets to minicopters?

I think that's out of scope for this plugin. Generally modular cars are really complicated compared to other vehicles, so I prefer to have separate plugins for them in many cases as it helps reduce the maintenance burden of a large plugin that has everything.

I believe there are several plugins that already add auto turrets to minicopters when they spawn.

• Minicopter options allows minicopters to just spawn with auto turrets
  https://umod.org/plugins/mini-copter-options
• Warcopter allows spawning preset minicopters with auto turrets
  https://umod.org/plugins/warcopter

I'm not opposed to automatically spawning turrets on vehicles or spawning preset vehicles with turrets on them, but that isn't the most flexible way to do it, which is why I opted for the approach of a command and API in this plugin. Other plugins, such as Spawn Modular Car, can always integrate with this plugin to spawn cars with turrets already on them.

This same approach that I used here could be applied to other vehicles. Since other vehicles are simpler, it would be reasonable to accomplish that in an all-in-one plugin for helis and boats. Likely each heli or boat would only allow a single auto turret which is probably plenty. Deploying could be done using a command, or by potentially dropping an auto turret item into the fuel storage container (I was thinking of using that approach for deploying code locks and key locks as well with my lock plugin). If you are interested, I can add this to my list of potential projects and I will work on it when I have time or when I'm interested.