You absolutely can do this. We did this just this past March, and My boyfriend is doing it again this trip in July. No one can tell you how to use the days you purchase on your ticket. As a matter of fact as recently as 3 weeks ago a CM on The Reservation line double checked for me that we were still able to do this. If you want to visit two parks in one day, and your ticket is not a hopper, it will simply use two separate days on your base ticket. We have done this multiple times. That is what
@ptnia was trying to say. I know this, because she is my mother

. She may be new to the boards, but is certainly not new to all things Disney! haha Hope this clears up all of the confusion. It is cheaper to add an extra day on to your base ticket (not stay an extra night at disney world) if you're only going to park hop one day, rather than adding on the park hopper to your ticket since you don't need it every day.