Straight up though you would not be able to declare an attack in the first place if your original armament couldn't fire at long range to begin with. So replacing black with red would be only possible if the ship started the attack within short range no?
Based on my first read of the Sato card, I read it as If I have 4 red dice while attacking, I can choose to replace up to 2 of those red with either black or blue dice or 1 of each. Before getting bogged down in the technical aspect of the wording, my natural interpretation of replace would be to substitute 2 dice with a different color before actually rolling them. Although it sounds really cool that I could roll, then say' those' are crap, make them 'these' instead and roll those seems like a bit of a stretch to me. Once again, the rules as they are this is possible, but seems to be lacking in the intention. As a casual gamer I would never assume that these would be rolled after already rolling the attack.
except then you are re-rolling, so you would need a re-roll ability.
The attack pool is the collection of dice before you roll them. Once they are rolled, they are results, and you have no dice in your attack pool to swap.