Quoting Mamai:
"Unfortunately, we weren't given an editor for game.orc. However, it is known that part of its code is present within the game's EXE file. Through some rather ingenious methods, I managed to launch it in a somewhat working version. It's too early to show it to the public (and it's not even certain that I'll be able to create a version that is stable enough to release for everyone), but I can show you what it looks like:

The image above shows the editor for game object parameters. Here's what the Model Editor looks like in the same editor:

In the game.orc editor, you can also edit races:

There's also some kind of sound editor there:

It seems I've managed to create a stable version of the game.orc editor based on the game's EXE file.
Installation: unpack the archive
http://www.multiupload.com/2AEC37CCIW into the game's directory and run runeditor.cmd
When starting, a window with an "OK" button will appear, and the regular Campaign editor will launch. You need to wait for the editor to finish loading, close the map that opens in it (if it opens, you don't need to exit the editor itself!), and then press OK. After a couple of seconds, the game.orc editor window will appear. You can minimize the script editor window, but don't close it.
First, you need to unpack all the game's orc files into a separate folder and open game.orc from there. A "standalone" game.orc will not open because it refers to the other files in the directory (XML files, animations, etc.). I haven't checked which files it needs, as I already keep all the game's resources unpacked.
I haven't tried editing game.orc or playing around with its modifications myself. But, it seems that the file opens, and then it can be saved, although the size of the resaved file decreases. I don't know why this happens; it might be a bug in the editor, or maybe I didn't enable something.
I figured out why game.orc was shrinking when saving. I wrote here "unpack all the game's orc files into a separate folder," but I didn't do it myself. That's why the editor couldn't find some of the gobj and other files in the directory with game.orc and removed the references to them when saving."
As you can see, the map editor is now not only a map editor but also a resource editor. Something like this already existed in HoMMV, but the editing capabilities were smaller: sounds/music/models had to be edited separately using third-party programs, while the editor only allowed you to create a mod to add them to the game. So, those who are against the current balance can now try to create their own version of HoMMVI ;)
Thanks to Mamai!