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

Is it possible to implement this within a reasonable timeframe/work hours/capabilities, etc.? After all, hints for regular heroes are already implemented; perhaps the same approach could be used here. But ultimately, the author knows best how difficult it would be to implement.

Implementing this would literally take a minute or two. However, at the very least, you should wait for HD 3.0.
However, as I see it, an experienced player would only benefit from this feature in identifying heroes who are not level 1 or who have artifacts, i.e., former enemy heroes.

Hey, is it possible to come up with, invent, or, well, I don't know, create something like a built-in chat in NDMod in the near future? Like the one used in VT. So that when NDMod is enabled, the chat is automatically activated, appearing either at the bottom or in a separate window, similar to the VT chat.

I'm not against such a feature. But I won't implement it myself. If someone provides the source code with an implementation using only WinAPI, I can easily integrate it with the heroes. In fact, I think I mentioned a long time ago that I don't aim to replace VT. Let ASM implement SoD gameplay instead