When equipped, do I have to use the effect or is it optional to choose an enemy ship at the beginning of the game?

"A Score To Settle" is not optional. The word "may" makes game effects optional, and the word does not appear in the setup portion of the card ability:

"During setup, before the "Place Forces" step, choose 1 enemy ship and assign the "A Debt to Pay" Condition Card to it."

Quote

During setup, before the "Place Forces" step, select 1 enemy ship and assign the "A Debt To Pay" Condition card to it. When attacking a ship that has the "A Debt To Pay" Condition card, you may change 1 [Focus] to a [Crit].

At no point does it give you any options other that which ship to select. You must do it.

Thanks for the answers

It's a hazardous card to use because you give the same benefit to the target that your ship gains against that same target. Sometimes you just don't want to give that large of percentage of the enemy fleet an advantage.

But the effect doesn't end when your ship dies, right?

If either the ship that is carrying the condition or the EPT is destroyed, it will end.

1 hour ago, Lobokai said:

But the effect doesn't end when your ship dies, right?

It only affects attacks made by one of the two ships against the other one. Even if it doesn't automatically go away, it can't have any further effect once one of the ships is out of the game.

2 hours ago, Lobokai said:

But the effect doesn't end when your ship dies, right?

A Score to Settle? The condition will remain in play but the upgrade only assigns the condition at the start of the game and the condition and upgrade only act against each other. The effect doesn't "end" when a ship dies but there would no longer be a valid target so it does become useless.

Sorry for the resurrection but i have a query regarding the A score to settle. If you have 2 ships with the Score to settle condition, can both ships select different targets and both gain the benefit on each ship? " When attacking a ship that has the "A Debt To Pay" Condition card, you may change 1 (focus) result to a (Critical) result.

2 hours ago, anythingbutaone said:

Sorry for the resurrection but i have a query regarding the A score to settle. If you have 2 ships with the Score to settle condition, can both ships select different targets and both gain the benefit on each ship? " When attacking a ship that has the "A Debt To Pay" Condition card, you may change 1 (focus) result to a (Critical) result.

The card is unique, sou you won't have 2 conditions.

1 hour ago, DaProfezzur said:

The card is unique, sou you won't have 2 conditions.

Ah, Thank you. I hadn't realised that as i'd been using an online squadron builder

On 2/20/2017 at 2:41 PM, StevenO said:

It's a hazardous card to use because you give the same benefit to the target that your ship gains against that same target. Sometimes you just don't want to give that large of percentage of the enemy fleet an advantage.

That's why I run it on (Rebel) Chewbacca. I get crits, you get crits ... oh wait, you only get hits.