I know that when you spend a Target Lock to reroll dice following an HLC attack that any crit results generated from said rerolled dice are kept. If you are using Calculation can you change an eyeball to a crit or is this a different interaction?

Immediately after rolling attack dice, change any crits to hits, and then after that, it's open to regular dice modifications. Calculation is just another dice modification. So you could reroll, and if you get a eyeball result, you can use Calculation to change it to a crit.

Same interaction.

HLC's de-crittening happens once, when you roll the dice. Your modifications happen later.

Among other things, you can't de-crit again after getting one through a re-roll even if you wanted to (like, say, you were against a Leebo, a ship with Determination, or near a ship with Draw Their Fire.)

In fact anything that could modify your dice to a crit works.

Lets say you rolled 3 eyes and 1 crit with your HLC at r3.

First you will turn the crit to a hit to satisfy the HLC effect.

Then if you had marksmanship, you can turn one eye to a crit and all other eyes to hits.

If you have Mercenary Copilot, you can turn the crit back on.

If you have both, then you can turn the the crit back on with the copilot and turn another eye to a crit with marksmanship and all other eyes to hits.

etc etc etc...