I think that the overriding principle is that you don't get to make free CA changes during the opponent's MPh unless you actually fire something (barring a successful motion attempt). If you change VCA without firing a bow mounted weapon whilst also changing TCA to fire a turret mounted weapon, you are violating that principle.
Why is changing the VCA and TCA simultaneously on a CMG shot getting something for free? The TCA always moves faster than the VCA. You agree a CMG shot could opt to change the VCA, if it has time to change the VCA it has time to change the TCA as well. Different controls operated by different members of the tank crew after all. Of course this all just down to game mechanics trying to deal with roughly modeling vehicles that are moving simultaneously in reality but move sequentially in the game, so really either interpretation is just as arbitrary or real…
Principles are nice, but in a rules dispute with another player doesn’t it come down to what the RB says and specifically COWTRA? It seems like the quoted sentence in D3.12 specifically allows a CMG shot to change the TCA
and the VCA - not “or”. Where is the principle documented in the RB?
EDIT: And another thought. One tank has its VCA and TCA aligned and pointed away from an attacker. Another tank has its TCA pointed at an attacker but its VCA pointed away from the attacker. In the first case the defender can fire
any one weapon (bow or turret) and get front armor pointed at the attacker. In the second case, the more prepared tank for the attacker, it must fire two weapons to achieve the same defense? That doesn't seem right... Again, perhaps just down to the limits of what practical game mechanics can achieve.