Modify Source/Insurgency weapon for all theaters

I want to tweak an Insurgency weapon, and have that change apply across all game modes, and not modify any other aspects of the game.

The only way I’ve found to do this is by creating a new theater file in my local scripts/theaters folder, and setting it in the console or server config with the mp_theater_override variable.

"#base" "default_push.theater"

"theater"
{
    "weapons"
    {
        "weapon_m18"
        {
            "weapon_cost"       "2"
        }
    }
}

This works, but it has to extend the default_push.theater in order to make sure that my custom theater applies on top of default_weapon.theater, and all the other theaters that are used to make up Push and the other game modes.

So if I wanted it to apply to the Occupy theater, I’d have to change that line to say "#base" "default_occupy.theater". I want to find a way to make only modify the default_weapon theater, without having to modify any of the game mode theaters, or having to manually tweak my theater every time I switch to a different mode.

I’ve tried creating a weapon.theater in scripts/theaters, but it didn’t seem to do anything. I also tried copying the stock default_weapon.theater to that folder, and modifying it, but that also didn’t change anything.

Is there a way to query for a variable inside a theater file, so can say something like "#base" "default_{$mp_gamemode}.theater"? Or some other solution?