the creative mode wouldn't be fun I think there should be a building mode where you take no damage and don't starve or dehydrate but you have to get your own resources outside of building mode. Building mode should be turned on and off in main menu and in game toggled with the buttons 'ctrl b' in game. You shouldn't be able to do much in building mode apart from opening chests, building and breaking. In building mode you don't get resources back from stuff you built if you break it.
I suggested creative mode due to the fact that they game saves aren't backwards compatible. I myself put over 5 hours of work into my save in v1.03 and sadly cannot play in that same world in the newer versions. Creative mode would be a quick way for users to quickly regain any lost progress.