Lin, it would depend on how close-fitting the full chaps are made if they fit over your winter boots or not. I have ariat zip front paddock boots (winter kind) and my 1/2 chaps do not zip well over them but my full chaps fit well. i don't see any reason why you couldn't wear both 1/2 and full chaps at the same time- I used to wear my tall boots under chaps. In winter around here the extra warmth the 2 layers would provide would be quite welcome, as long as your full chaps are cut wide enough to fit over all that.

I have worn long johns under a set of ancient Patagonia wool riding tights (they no longer make them) with the full chaps over all that.