May I have a clarification regarding whether or not Krassis Trelix's ability, "When attacking with a secondary weapon, you may reroll 1 attack die," can combo with Cluster Missiles allowing for two potential rerolls?

The text on Cluster Missiles states that you "...perform this attack twice." Does this imply that each attack is completely separate and triggers Trelix's ability separately? I assume that you only get one reroll as the cluster missiles are activated once, but I would appreciate some insight.

Also, if I were to use the Heavy Laser Cannon in conjunction with Mercenary Copilot, would I be able to change one of my hit results to a crit result at range 3 after the HLC's immediate effect resolves?

The wording on the HLC states: "Immediately after rolling your attack dice, you must change all of your Critical Hit results to Hit results." Does this effect occur once immediately and then resolves, or does the effect persist until after all hit and defense dice are resolved?

Yes, his ability would work with both cluster missilie attacks as each is treated as a separate attack.

The Heavy Laser Cannon (HLC) immediately converts all crits to hits then you can use the Co-Pilot's ability to convert one hit to a crit.

So Trelix making a HLC attack at range 3 and would roll 4 dice, his ability would allow a reroll of one die. All crits are converted to hits, then his co-pilot converts one hit to a crit.

PS: Welcome to the forums!

So Trelix making a HLC attack at range 3 and would roll 4 dice, his ability would allow a reroll of one die. All crits are converted to hits, then his co-pilot converts one hit to a crit.

Not sure how explicit you're trying to be with the timing here, but this isn't quite right.

You change all {Critical Hit} results to {Hit} results immediately after the initial attack roll. After that, the HLC's ability does nothing. So any modifications, including rerolls, will stand.

So it should be:

...Trelix making a HLC attack at range 3 and would roll 4 dice. All crits are converted to hits, his ability would allow a reroll of one die, then his co-pilot converts one hit to a crit.

Look at it the following way: HLC does not refer to the physical action of rolling dice (1). It refers to the roll attack dice combat step (rulebook page 10). During or after (2) that step, you change all {crit} to {hit}. Then you proceed to the next step, modify attack dice. Krassis ability, mercenary copilot, focus, TL and other effects resolve during that step.

(1) If it would it had to trigger after rerolls.

(2) We do not know if it happens during one step or between two steps.