why dont you just do 810? I dont see the point of this...
sorry to be harsh - but why are you actually bothering if you cant follow it? why not choose a plan more suitable to your lifestyle and stick with it?
changing all the time is leaving the door open for excuses, slip ups, frustration, and not acheiving what you set out to.
as for interchanging, i am only just starting cd, and I know that you are not supposed to. I know some say 'its ok' but it isn't ok really. your body needs continuity. so yeah you may lose weight, but you will never break the control that food has over you this way.
good luck, but my two penneth, is stop messing yourself up like this and get on with it properly.