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 haven't explored this direction, so I can't say anything concrete. At a minimum, I won't have time to look into this topic for at least 3 months.

2)

The second question is on a more global scale.
The capabilities embedded in the template description file (rmg) are insufficient for a full implementation of a mirrored template. Specifically, there are not enough options to replace towns with teleporters. When building the template, you have to assign a specific racial affiliation to the town that needs to be replaced. The race of the town also determines the racial affiliation of the entire zone (dwellings, creatures in the pandoras) and does not allow for a random race for the zone.
...

I am not familiar with templates, their capabilities, or the RMG 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 am almost unfamiliar with working with the RMG and I don't control the map loading.
However, I can do a lot with an already loaded map.
What principle is generally used for creating mirrored maps? Is the top copied to the Dungeon with corresponding changes, or how?