I was thinking about this and was wondering if it actually existed. The idea is for a story based game similar to Arkham/Eldritch horror where the core rules of the game are supplied. But the player can decide to be creative and do things no listed in the rules. In this case, he makes up the rule on the fly or just make it work.
For example, a player could make a diversion to draw enemy units out. Maybe there is no AI rules to handle this, but since it's a solo game so it cannot be unfair for other players, so you could just select a random unit to fall in the trap. But afterward the combat resolution follows normal rules.
So yes players could cheat more easily, but maybe explaining them that the key to a good experience is to stay in flow between challenge and boredom could help reduce cheating.
Else some rules could be made up by the community. For example, a player could have designed some bribing rules that anybody could reuse. One thing I intend to do is give all components of the game some generic values from 1 to 5 so that it can be checked against a single die roll. So if you come up with a new idea, and you want to resolve it, roll 1D6 against any game component you want to affect to know if it works.
Did anybody attempted something similar before?