Latest FAQ for Garven Dreis (Page 10)
A ship may spend a focus token during an attack even if there are 0 focus results to change (including an attack where no dice are rolled, such as when a ship has a faceup Blinded Pilot Damage card [original Damage deck])
And
Spending tokens (page 6)
When attacking, players may spend target locks and choose to reroll 0 attack dice.
Additionally, players may spend a focus token even if they do not roll any results.
When defending, players may spend focus tokens even if they do not roll any focus results and may spend evade tokens to add evade results in excess of the number of hit and critical hit results.
HSCP
When attacking with a primary weapon, the defender must spend 1 focus token if able.
When defending, the attacker must spend 1 token if able.
Given the FAQ entries that say that the rules permit you to spend a focus token even when you do not roll any focus results, it would seem that the only time you are not able to spend a focus token is when you do not have one.
In other words, if you have a focus token and you attack, or are attacked by, a ship with HSCP, you will be forced to spend the token regardless of what you roll.
Make sense?