HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

1) Well, I've said many times that theoretically, you can do anything with the heroes. Specifically regarding this issue, I don't think it's that complicated.

I believe that indicating the length of the hero's route fits organically into the concept of the mod as an interface mod. And such a feature would be very useful. Unfortunately, it cannot be implemented using the map editor – only by modifying the executable file, and I'm not very good at that, to put it mildly.

I'm not familiar with templates, their capabilities, or the map editor itself. I also don't know anything about mirrored maps or the existing implementations. Therefore, I didn't understand what needs to be achieved in the end and didn't understand the problem.

In any case, I'm almost not familiar with working with the map editor yet and don't control the map loading. However, I can do a lot with an already loaded map.
What is the general principle for creating mirrored maps? Is the top copied to the Dungeon with corresponding changes, or how?

Yes, the general principle for creating a mirrored map is as follows. If you're interested, here's a link: http://zalil.ru/30721992. The readme file briefly describes the creation process.
There are no particular problems with creating the mirrored map itself. The program works, and people use it. The problem is integrating it into the game so that you can start on the mirrored map just like on a regular template. But this is, in principle, a solvable problem.

The question is different:
When creating a random map, the generator divides it into zones (respawn areas) according to the structure of a specific template. That is, each cell of the territory belongs to a certain zone, and accordingly, it is assigned the soil type of that zone, and an object belonging to the zone can be located on it.
But when the generator creates the map, the map format itself no longer contains information about the belonging of cells to a particular zone. That is, by programmatically analyzing the map, we cannot know to which zone a particular cell or object belongs. Only in a specific case, if different soil types are set for all zones, we can judge which zone an object is located in based on the soil type under the object. Or, specifically for cities: if a city of a certain faction exists only in one zone, then when we encounter its description in the map format, we know exactly to which zone it belongs.

That is, to create a structure of connections (teleports, elevators) between the two planes of a mirrored map, information about the belonging of a territory cell to a specific zone would be very useful. Currently, when creating mirrored templates, we have to put up with some limitations. First of all, it is impossible to set a random faction affiliation for a zone in which there is a city that needs to be replaced with a teleport.
Currently, the city parameters that we can influence through the rmg file are as follows: belonging to a player, city faction, whether or not there is a fort. Information about the zone number to which the city belongs would allow us to create a structure of connections between the planes of the mirrored template with virtually no restrictions.

I understand that this question does not relate to the HD mod, but I would be curious to know your opinion on the possibility and difficulty of solving it.