How to change a creative world in Minecraft into survival?

Details:
I'm using Minecraft Pocket Edition
I'm not Jailbroken
I'm using an iPhone

Create a new survival world titled the same as the world you want to switch. Get root explorer from the android market. Navigate to sdcard/games/com.mojang/minecraftWorlds/ name of world created above. Copy the level.dat folder from your new survival world created. Find your old creative world and replace it with the copied level.dat folder. Make sure to completely quit out of minecraft, do not run it in background.