Jean,
That is one of the hitches when you plan to dine at a Walt Disney World restaurant that is located
inside of one of the parks. You have to gain admission to the park first. So if you are not getting park hoppers, and you make Epcot your park of the day, no, you would not be able to get into the Magic Kingdom to dine at Cinderella's Royal Table. To do so you would have to add the Park Hopper feature to your tickets.
But I have a solution. If you are in Epcot, and really want to get that Princess experience, try the
Akershus Royal Banquet Hall within Epcot's World Showcase. The food is very good, the princess experience is comparable (in some ways better, as you sometimes get a broader array of princesses) and it will only cost you 1 table service credit, as opposed to the 2 that you 'pay' at Cinderella's Royal Table!
I hope that this helps? Write me back if you have any follow-up questions. I
LOVE dining questions!
Have a magical (and delicious) vacation!