We used to bring and fit the whole kit, including aerials and actuators.
This was in the days before I was a pilot and I can’t remember what the exact legal situation was, but on our installations, the aircraft engineer associated with the helicopter signed it all off.
If we needed a different aerial for a particular reason, we just swapped it over.
So I think the basic mounting(s) must have been CAA approved but the exact aerials and layout used on a particular day were not set in stone, as long as they were mounted securely and wirelocked etc.
What project do you have in mind? I used to do this sort of thing a lot.