I wanted to change things up a bit with my world. I remembered that in my tutorial on how to recover a minecraft world I mentioned that you could but the world seed would be changed - and that was a bad thing.
Addendum: I went back and looked to discovered I didn't actually mention that the seed changes.
However, that got me to thinking; I could deliberately do that to create different regions in the world! Hey now! what a great hack that would be!
So this is what I did:
I backed up the world with a simple copy/past and saved it as "World5 - copy" (windows appends "-copy" to the name if you just paste in the same folder as the original - which I did).
I then created a funky new world with the gargamel seed. To do this simply create a new world and in the seed type "gargamel," save the world and exit. (Any seed will work but this one is famously good)
Now go into the gargamel world and copy the "level.dat" file (it holds the seed).
Return to your saved world (in my case World5) and replace that worlds level.dat with the one you copied.
If you want to keep your swag open an inventory editor first then save again after pasting.
Now start your original game and go explore!
This is a great way of starting a new world without losing your old one. Notch claims he is going to enable players to move their spawn areas in the next update.
My results were pretty cool:
The world isn't exactly gargamel but it's very different than what I would normally find.
I explored off the end of the Red Road and am now completely lost. When I find my way back I'll upload a new map and saved game.