We have developed an LLM-based agent for manipulation of text-based game environments, and generative agents within them, to convincingly alter the genre-setting of a game with respect to pre-existing lore and in-game mechanics. We contribute a novel, tested, LLM-based agent for this purpose: a `Setting-Switcher' agent. This agent opens a range of creative applications and possibilities: our agent can be used as an ideation and productivity tool, deployed within a player focused in-game feature, and used in tandem with other state-of-the-art technologies for application in visual game environments. Our investigation has highlighted the effectiveness of LLM-powered agents beyond conventional text generation and task completion: showcasing their value in crafting coherent narratives, portraying complex characters, and facilitating emergent storytelling within game settings.