The CE free month for a subscriber

I had a question about the CE code, and the free month of subscription it gives. I'm already a subscriber; if I add the code, I assume the free month is just wasted? Or does it "save" until you unsubscribe?

On that note, if I unsubscribed and added the code, would it kick in after my paid time runs out, or just start immediately?

On *that* note, if I unsubscribed, added the code, then subscribed again immediately, would I get an unpaid month sandwiched in?

Thanks to anyone who replies!