"HW rulez" mod (add-on) for HoMM3.

I apologize for the noob question, but what is the connection between the save file format and gameplay limitations? That is, why modify the save files?

We need additional information about whether the player had a Town Hall of the required level built. For example, if a player's castle with a Town Hall is captured, they can still use scrolls.
This information needs to be stored in the save file.