When you go to create your world, hit the world type button where you choose things like Amplified or Superflat.
I can't remember the text, but one of them is something like Customize.
Hit that, and then you will see a new screen, hit next till you get to the very last one.
There will be a text box at the top. Delete everything that is in it and then paste my code in there, Hit the Use Preset button (Or whatever it says) at the bottom and then create your world.
The nice thing about this is Minecraft stores the preset values, so once you paste my code in there, it will always be there, and you can use that preset again later. You still have to do all the other steps though to get MC to use that preset.
//Sorry I couldn't remember the exact button titles.