I also want to say a few words:

2. Convenience for the players themselves. Let's say you want to play, but the activity on your native forum has stagnated, while a major tournament is starting on a neighboring resource. Naturally, the player signs up, but in the heat of the competition, they might forget and start playing "by their own rules." Even if it doesn't lead to a scandal, the game is still ruined. Unification would allow players to play seamlessly on different resources, which would raise the status of tournaments to the benefit of both communities.

So that this kind of nonsense doesn't happen, you can simply discuss it in a small group and agree on common rules – why make it so difficult?
And if you are already thinking about the rules, here is a request:
If you compare the rules between fixed and random games, the fixed game has fewer restrictions, and there might be a couple more nuances. So, maybe you could add a few points to these rules with a note "fixed only" and the same for points that are not suitable for fixed games (for example, building a Grand Magus for using scrolls) - "random only"? I'm ready to delve into this if you like the idea:)