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Example of a question for which I have not found a definitive answer in the fair play rules: "Is it allowed, while repeating a move 'as accurately as possible', to move 1-2 tiles further if a hero with more movement points arrives, for the purpose of scouting or any other purpose?"

And the definitive answer is what experienced judges should provide, who are capable of assessing the degree of influence a given maneuver has on the game's outcome in each specific game situation. Because there is not and will not be such a thing in the rules, since it is simply not realistic to stipulate everything in existence.
But you can occupy yourself in your spare time - create a Talmud, stipulate everything you deem necessary, and submit it to the community for review. The official HotA rules have long needed tidying up (look, for example, at the trade rules - I have never seen anyone conduct trading according to those rules).
And the rules on HeroesWorld, it seems, have not been properly updated for a long time either - there is no one to do it.
Go for it; if it's constructive, it will be better for everyone.

Added 5 minutes later

Or what to do in the opposite situation, if a hero with fewer movement points arrives and it is not possible to bring the army in the chain to the main hero, causing the main hero to step back and be unable to remain in the same position as before the disconnect? This could make it impossible to position for the opponent's attack. Is this considered an accurate repetition of the move?

If it concerns deciding the fate of the match, then reload as many times as needed, and repeat the move as many times as needed, until a situation acceptable from the judges' perspective is achieved.