The full game is editable via the built-in level editor called Ginked, that is shipped with the game. You can modify every scene in the game, build new levels and also start a completely new game from scratch.

To get you started we put together a description of the core features and basic functionality, that you can find on the Wiki pages for Secrets of Rætikon: http://secretsofraetikon.gamepedia.com/Ginked

Let us know what features you want to have explained in more detail if you get stuck somewhere!