If you still have a focus token after the modify attack dice step and an opponent uses sensor jammer, are you allowed to use the focus to modify that die?

Sensor Jammer

When defending, you may change 1 of the attacker's hit results to a eye result.The attacker cannot reroll the die with the changed result.

Main rule book

Step 3 modify attack dice (page 11)

During this step, players may resolve abilities and spend tokens that allow them to modify attack dice. This includes adding die results, results, and changing die rerolling dice (see “Modifying Dice Results” on page 12). If a player wants to resolve multiple modifying abilities, he resolves them in the order of his choosing. If the attacker and defender both have abilities that can modify attack dice, the defender resolves all of his abilities before the attacker

So yes the attacker can modify the result using a focus. He just cant re roll any dice.

However your question was can you use sensor jammer and focus after the modify attack dice step. Sensor Jammers have to be used in step 3, they can not be used in a later step.

I'm pretty sure he can reroll the jammed die. It wasn't rerolled it was modified. Or does changing the facing count as a reroll?

But the important bit is that the attack die would be changed by the defender first, so the attacker could still focus or not as they wish.

I'm pretty sure he can reroll the jammed die. It wasn't rerolled it was modified. Or does changing the facing count as a reroll?

But the important bit is that the attack die would be changed by the defender first, so the attacker could still focus or not as they wish.

You can't reroll the jammed die because the Sensor Jammer card itself says it cannot be rerolled.