I noticed when I put my sugar rush texture disc on the base I got the message "unlocked in the toybox". I could not figure out what that meant as checking to toybox and the themes there was nothing sugar rush there, note I had taken the disc off the base after changing the theme. Last night I had an idea and put the disc on the base in an empty toybox. This time I selected no to the set your world to this theme box and kept the disc on the base. I then selected a terrain block and picked the pallet option and in the textures was the sugar rush ground.
I know I wasn't the only one wondering about this, so here is the answer. I believe this is how we can mix the themes as well like disny did with the Tron/Sugar Rush toybox.
I hope that I put this information in the right place.