If I understand your requirement correctly then when you are in the configuration page for that activity and in the user interface tab just click the + button on the top left hand side and that will add another page for you which you can then edit.
Different button mappings for each page in an activity activity is not possible.
But what you could do as a workaround is to create a separate activity with just one page an the desired button mapping. Then you add all of these sub activities you created for each page to a main activity and add commands to the first page to start these activities. When you search for the name of each activity you will see commands to start and stop these activities. Also add the main activity to all sub activities so that you can go back.