"HW rulez" mod (add-on) for HoMM3.

It would also be good if the opponent could see the settings made by the host. That is, if you banned a certain creature or set the starting level to 2, you wouldn't later pretend that "it just happened that way." These settings should be transparent to both players, and there shouldn't be any deception.

Yes, that's how it is now: the host sets the settings, then the client sees a window with the selected options and can agree or disagree. If they disagree, the game won't start.

Is it technically possible to replace one-way paths? This would be the most painless and most pleasant change for the community.

Sav knows a lot about map generation; I haven't delved into those details yet. I can suggest replacing one-way paths with 2 inputs, 2 outputs with 4 inputs, 4 outputs, based on the "War of the Ancients" expansion. It's quite simple to implement.

If you dig deeper, in theory, you could replace one-way paths with two-way paths while keeping their graphics, but I feel that it's not that simple, and it's not worth counting on such an option in the near future.