[Guest]

Nope, don't think it is possible (due to how the game does loadouts) and also historically, such aircraft would have carried ammo (though possibly reduced). Especially with aircraft using rockets or large calibre cannons, the MGs were used to assist in aiming at ground targets.

I think that the P-51 pack that is coming out does have such options for reduced or varying ammunition loads depending on other ordinance. But as such, default aircraft cant have the ammo altered (either all or none)