Q: Can a TIE Advanced x1 that rolled 1 additional die from Advanced Targeting Computer spend the lock later in the attack? If it does, can it change 1 <hit> into a <critical hit>?
A: While performing an attack, a TIE Advanced x1 can spend its lock to reroll attack dice after rolling 1 additional die.
It can also change 1 <hit> result to a <critical hit> result and then spend the lock to reroll attack dice. However, note that it cannot change 1 <hit> result to a <critical hit> result after spending the lock, as it no longer has the defender locked.