It's not cheating is it...

[Suicide Junkie]

You might have a point here. But in that case I would say if the creator of the mod is a player in the game, then him trying to set down such a rule is dirty pool. He'd be the only one that knew how things worked.

If this were the case, you would have to have a third party create the mod.

In fact, I had an idea for a mod where the physics of the universe would change every 10 turns or so, by using a new mod each time.
Shield generation might become hard or impossible, all ships might be completely cloaked for a few turns, weapon strengths, supply usages and ranges might vary. Whatever comes to mind. A special facility might be buildable, who's description indicates what changes are likely for next turn

This would all hinge on the mod-modder not being in the game, AND players not peeking at the tech trees.