What will happen if I take a model from Heroes 6, rename it as in Heroes 5, and simply replace it? :DDDD
Nothing will happen!
To achieve the desired result, you need to use a utility (it is paid, but the lifetime license and extensive format support are worth it) from the respected Zoltan Karpathy - 3D Object Converter
That is, the model's mesh can be saved in .3ds format and then worked with. Next, you need to save the result in .mb (Alias Maya 6.0 - also paid, by the way, you can get a license through a downgrade), and then, using the illustrated step-by-step tutorial from my page based on the method of the respected CrazyPill, obtain the model's mesh in the format of the 5th game, and at the same time, it will be formed in the Granny2 .gr2 format.
Added 1 minute ago
I just downloaded Photoshop 6, that's all.
The 6th version can also work with .dds

Added 2 minutes ago
Um, what's wrong?
The names of the previous games will cause confusion!

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