Hello blond_knight! There isn't a scenario editor, but you will be able to create your own scenarios for the game. The option to add user-designed scenarios will be made available after the game is released for MAC. The MAC version is close to release, if I'm not mistaken.
As a designer of scenarios for the game, I will be available to help any and all who want to dive into custom scenario design. The method takes a little getting used to, but once you understand how it works, it becomes easy enough. There is a help document that explains the basics of scenario design, which will be made available when the time comes. I am also considering writing a tutorial over the holiday break that will explain scenario design in greater detail.
Thanks for your interest!