I Hate This New Update, Except Large Biome, This Isn't Single player Anymore, I Miss It, Mojang, Notch, Jeb, Do Something, Make Me Feeling Bad, I Am Not Able To Cheat Or Fly or Anything, And Then I Got A Server Error........
To cheat, just make a cheat world (this include flying). This is still singleplayer, it just runs a server when you play (though you can have friends over).
Snapshot 12w19a is Ready For Testing!