Currently this can only be done via mods. As kju mentioned on Arma 3's Discord: "cfgActions can be modified via configs but not via sqf"
But loading mods can become a problem for mission makers who make vanilla/DLC missions without mods or for missions already dependent on too many mods or modding incompatibilities with future patches/other installed and enabled mods.
Arma 3's Default addActions such as the heal wounded action that appears even on wounded enemies and can cause interference with custom Medical Systems, custom Melee Systems and/or scripted/modded alternatives for many of the default systems.
Other example of Action Menu options that pop up is when having different ammo times for your current weapon, and such extra options end up cluttering that action menu. On some missions that action menu is already pretty cluttered and so it would be super helpful to let the mission maker disable this action at discretion.
The functionality could by exactly like the showHUD[] Description param:
showDefaultActions[] = {
1, // Heal Action on wounded Friendlies
0, // Heal Action on wounded enemies
0, // Heal Action on Self
0, // Reload Weapon with XX type of Ammo
1, // Get In Vehicle
1, // Get Out Vehicle
1, // Put out/Start Fire
1, // Climb Ladder
1, // etc
1, // etc
1 // etc
};
Update based on the discussion on Arma 3's Discord Feeback Tracker Channel:
kju also suggested: "Probably better would be a way to disable them for entities altogether and script the still needed actions instead"
As Dedmen asked how ACE removed these actions [KP] veteran29 replied: "we change item type of FAK to not be a FAK anymore".
All illustrious participants Leopard20, Sparker, kju and of course [KP] veteran29 suggested a scripted solution rather than my original suggestion of a Description.ext param.
All involved did acknowledge that having such functionality would be very helpful for mission makers and even modders and mods who use workarounds that sometimes even compromise their modularity/functionality/customization options.