http://prntscr.com/khk1wyI wanted to replace the swordsman with the 2004 version from the Heroes alpha or the inquisitor, but the game completely refuses to work with geometry files. Is there any way to force the game to use them?
No, of course not – you can't directly use them because the format is different!
But if there is a strong desire to use that version because of the helmet, then for your own purposes, you can modify this creature from the NCF project – NCF – Axe Man:smile13:

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Неудачное планирование ведёт к неудаче ...
NCF - мод, добавляющий дополнительных существ в HeroesV 3.1