If the countess is wise she will not pay in such a situation, the baron will know this and he will choose not to modify his source code. But it is a choise, the universe permits it.

Now this is a game of signalling -- to lie or not to lie, to trust or not to trust (or just how to interpret a given signal). The payoffs of the original game induce the payoff for this game of signalling the facts useful for efficiently playing the original game.

You don't neet to talk about "modified source code" to discuss this data as signalling the original source code. (The original source code is interesting, because it describes the strategy.) The modified code is only interesting to the extent it signals the original code (which it probably doesn't).

(Incidentally, one can only change things in accordance with the laws of physics, and many-to-one mapping may not be an option, though reconstructing the past may be infeasible in practice.)