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

Could you please tell me if it's possible to disable the interruption of simultaneous turns when players attack each other? And if not, is there a way to modify this?
Thank you!

There's no point in doing that; Heroes is a turn-based strategy game, and the whole idea of simultaneous turns is that players can take turns at the same time until a meeting is possible. But there's another problem: sometimes, simultaneous turns start to get interrupted in the early turns, even when both players haven't even left their starting areas, and a meeting is impossible. At the same time, if you load an auto-save and extend the simultaneous turns, they usually get interrupted again on the same turn.