If you change the configuration after the airplane is balanced i.e. armament or fuel tanks you in fact change the cg. The plane must be rebalanced to be safe. In the real world we had charts to show the cg with different weapons/tanks loads as they had been flight tested. The old AF F-4C/D was a good example. A slick jet (no external stores of any type) had a cg that was at the back limit. We normally flew with empty pylons just to get the cg farther forward and make the airplane more friendly. If you hang stuff on your model you need to balance it.