"Immediately before you reveal your manoeuvre, you may perform a free boost or barrel roll action.". so suppose i am stressed but am doing a GREEN maneuver? am i allowed to do the free "Sabine" boost or barrel roll? also just to reaffirm if I do a Barrel roll first I cant do a Barrel roll as my action. ?? as that would be doing two of the same action? thanks again..

No; because you are stressed. You cannot perform actions whilst stressed; regardless if they are free or not.

And yes, to your second question: if you perform a free BR, you cannot perform another one as your action for that round.

thanks

Special note for "Chopper" who will allow you to take an action while stressed, along with a damage.