Of course right now....there is no way to save your content, and i think with the research going on.....its for the best
Sooooo, you have to actively hack your copy of the game that took 4 1/2 hours to download, risk losing everything you've done on Xbox Live for all your life to a potential ban, and not be able to play with friends? Just so you can play offline, and not save? No thank you. There's very little point.
If anything it may raise the concern for lack of offline modes. Without split screen, there is little reason for custom games offline, but forge has obvious reasoning.
Right now there isn't any saving. Not to say there wont be. Plus I don't condone doing it if you are not comfortable with it. Right now its used strictly for testing. And serves no other function