As above - the objective introduces a 'special rule: When a squadron with Bomber or a ship is attacking, it may spend 1 die with a [hit] icon to flip 1 random facedown damage card on the defender faceup'.

The rules don't really seem to establish when you would 'spend' an attack die? The closest thing I can think of is the "Modify Dice" option in step 3 of the attack sequence: "The attacker can resolve any of its effects that modify its dice". In this case, 'spending' being the modification. And that would appear to happen before step 4, where the enemy would spend defense tokens.

That's exactly when it happens.

{Spend} is a Mechanic of Modifying Dice.

The rules are actually specific on that matter, as to what spend is.

- That is why Fletchette Torpedoes cannot be scattered

- That is why Sato's wording had to be cleared up (as Replace was not specified as a Modify Dice mechanic, like Add, Cancel or Spend is)

As you said,

3. Resolve Attack Effects: The attacker can resolve attack effects as described below:

◊ Modify Dice: The attacker can resolve any of its effects that modify its dice. This includes card effects and the P command.

When you thusly check page 7, you find:


Modifying Dice

Dice can be modified in the following ways by game effects:

• Reroll: When a die is rerolled, the attacker picks it up and rolls it again. A die can be rerolled multiple times.

• Add: When a die is added, roll an unused die of the appropriate color into the attack pool.

• Change: When a die is changed, rotate it to display the indicated face.

• Spend: When a die or die icon is spent, remove that die from the attack pool.

• Cancel: When a die or die icon is canceled, remove it from the attack pool.

Shameless plug that answers this very question!

Before.

During the Modify Dice step.