Shameless Charlatan

The copy effect doesn't have a duration. It lasts until the commander leaves the battlefield, though another copy effect with a later timestamp (perhaps from a new activation of the ability granted by Shameless Charlatan) would override the effect for as long as it's active.

An effect that checks whether you control your commander is satisfied if you control one or both of your two commanders.

If something refers to your commander while you have two commanders, it refers to one of them of your choice. If you are instructed to perform an action on your commander (e.g. put it from the command zone into your hand due to Command Beacon), you choose one of your commanders at the time the effect happens.