If you want to edit or add theses helicopters to appear in the skirmish menu into your vanilla/custom factions then is really simple:

1) Head towards “C:\Program Files (x86)\Steam\steamapps\workshop\content\302670\2960079482\resource\set\multiplayer\units" and open vehicles_mh6.set file with notepad++ or any text editor program.

** Keep in mind the path may very for each user but that's the default one...**

2) Once you open the vehicles_mh6.set file, you can change the faction you want theses vehicles to appear by editing the s(“factionName”) to your desired faction. You can duplicate these three lines and edit it as well.

3) Save any changes and start the game.