So Bossk can change a critical to 2 hits BEFORE dealing damage.

If I am attacking at range 3 using a Mangler Cannon and have a Mercenary Copilot can I use those card abilities to turn those hits into 2 crits?

Effectively using the abilities to turn 1 crit into 2?

No. The trigger for Bossk's ability is, "When you perform an attack that hits." This means his ability is applied after the "Compare Results" step of an attack (Step 6 in the attack timing chart) since that is when you determine whether or not the attack hits. Mangler Cannon's ability and Mercenary Co-Pilot both modify dice in the "Modify Attack Dice" step (Step 3 in the attack timing chart) which is before comparing results. By the time you cancel the 1 crit and add 2 hits using Bossk's ability, the timing window for Mangler Cannon and Mercenary Co-Pilot has already passed.

No. The trigger for Bossk's ability is, "When you perform an attack that hits." This means his ability is applied after the "Compare Results" step of an attack (Step 6 in the attack timing chart) since that is when you determine whether or not the attack hits. Mangler Cannon's ability and Mercenary Co-Pilot both modify dice in the "Modify Attack Dice" step (Step 3 in the attack timing chart) which is before comparing results. By the time you cancel the 1 crit and add 2 hits using Bossk's ability, the timing window for Mangler Cannon and Mercenary Co-Pilot has already passed.

OK, so what you are saying is that I can use the Mangler Cannon or Co Pilot ability to turn a hit into a crit AND THEN use Bossk's ability to turn the crit into two hits ..?

Bossk works like this:

You're comparing dice. You have 1 crit result, 1 hit result. Your opponent has 1 evade result, canceling out your 1 hit result.

Your attack hits.

Then, when you go to deal damage, rather than deal 1 crit, you can trigger Bossk to make the target instead take 2 regular hits.

So you can create a crit result during the modify dice step using Mangler or Co Pilot, but Bossk doesn't trigger till after comparing results.

Mangler and Copilot happen during dice modification while you are attacking. You would get 2 crits if you had 2 hits.

Bossk triggers after your opponent defends and theres still a crit left over. At that point, instead of having him suffer a crit, you can make him suffer 2 hits. You cant mod those 2 hits because this is in the Compare Results step