if you are thinking of changing the look and feel that much this may not be a good thing.
are you talking about adding new pages and adverts and such or are you talking about being able to change the entire design and layouts yourself.
ideally you should choose a layout, select a theme. and then you would have designated blocks in that theme that are easily changeable. Aheadworks do some good modules that allow easy changing of ads and banners. with regards to your theme. This is part of your whole brand so i wouldnt say you want to be changing that all the time.
What are you envisaging doing?