It is possible! Now you can play with your friends without fear of having the game ruined for them or vice versa. I honestly don’t know why this isn’t a menu option, but mathlas.dk writes with a solution:
You CAN start over.. (it’s a bit advanced yet easy) :D
If you’re not familiar with the developer console read this:Enable Developer Console in:Options -> Keyboard/Mouse -> Allow Developer ConsoleThen go back to the main menu and press the ‘~’-key.(if the key isn’t working, like if you don’t have an english keyboard, then go to:Options -> Keyboard/Mouse -> Edit Keys/Buttons -> Miscellaneous -> Toggle Developer Consoleand set it to a key that works, I just used F1).
Open up the console and type:
and press the enter-key and exit the console.
Now when you host (invite someone to play) a game, you start from stratch! :)
The link above to StackExchange Gaming has a more detailed explanation.