I don't know, if the byte modification works, I might be able to try adding 2 top spells and test it, but whether they will be automatically added to each map is not certain. So, what is the byte number and its values?
Here, the maximum possible number of spells has been increased from 353 to 354, i.e., the number of skills remains unchanged, only the spells!
Here are the addresses: 00446с91 and 0044bdc0.

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