[Mod edit: RL tangent despite mod request]. While that rings true of many mechs in BT as well, some variants change the base design so radically that they no longer have that high parts commonality. Again, I'll use the example of the Hunchback 4SP, which drops the RT mounted AC20 in favor of mounting an SRM6 in each side torso and an extra Medium Laser in each arm. Modifying the arms to mount an extra laser isn't terribly hard, and modifying the AC20 mount to feed an SRM is difficult, but not impossible. Modifying the normally empty left torso to mount an SRM6 and all the systems required to make it function, such as its ammo feed, requires considerably more effort than your average merc company is capable of. With the Argo at full functionality it would be possible, considering the thing is a flying mech factory, but in the Leopard, or in the Argo without all of the mechbay upgrades to bring the factory components online, you'd probably have better luck convincing a Clanner that Stefan Amaris did nothing wrong