When MCing a figure, can I turn off optional powers?
Does this count as the 1 free action?
When do the powers return, the end of my turn or the end of my opponents?

I don't know about turning powers off while you have control of them. However, if you could the power comes right back as soon as you are done w/ your action and he is no longer a friendly figure to your team. So in essence it's pointless. You can't say i'm taking over so and so Brick turning off impervious then running him over to my brick...action finished he is now an enemy agian. Now, your brick attacks but he still has his Imp/Inv. on. Even if you still had control you couldn't attack him b/c you can't attack freindly figs. So it's hopless...just forget about it.

Any optional powers can be turned off, and remain off until the end of the current turn. Turning off optional powers is not an action of any type.