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

Is there a possibility to add any new gameplay features? I mean, for example, after building a market and a resource depot, add another building, something like a messenger (post office), to allow sending artifacts and/or troops to allies? (of course, the transaction should not take 1 day, but, say, 3, 5, or 7 days. Maybe in the form of a plugin for the offline game?