Heroes 5.5 WarGame Edition - Tactical Edition.

Generally, I prefer the simplest solutions, and once they are implemented, we can think about improving them by replacing them with more exotic bonuses, having a live comparison of their effects. Undoubtedly, the most interesting solution, assuming it is possible, would be a flexible change of racial or elven rituals, allowing you to spend 25% of your turn to change your sworn enemies. To do this, you would need to somehow remove the guild from the city and simulate the hero touching it, and upon exiting, return the hero to the old location on the map.