A festival is a guest; a government rewrites the tax code
Events should feel like a tent in the town square, not a coup.
When a season introduces its own court for disputes, its own language for fairness, and its own currency that touches the main economy, the player must carry two constitutions. Most people will not. The honest approach is a visible sunset: a season must be able to pack up without leaving a secret police of modifiers behind in the main loop.