Missile rule clarification
Missiles change a die into a '6' only. A missile can never modify a die to anything else.

Perhaps a non-spoilerific example might clarify.


An attack roll on a Ammo Shortage territory is 6,5,1 versus a defense roll of 5,5. The defender's high die is reduced by 1 because of the Ammo Shortage's -1 modifier making their roll 5,4. The defender uses a missile on the '4' making it an unmodifable '6' (Ammo Shortage can no longer affect it), and the attacker loses 2 troops instead of the defender (6,5,1 vs 6,5 after missile instead of 6,5,1 vs 5,4 before missile)