NHF – new heroes for Heroes V 3.1.

What do you mean by "affecting a spell"?
In principle, it could be linked to Chaos magic and placed on the fifth level with a chance of appearing in the Inferno castle (like with the "Unholy Word" spell).

Spells are not copied, just like special abilities. You can only modify existing ones, which means it will be necessary to change the regular curse word and Helmar's special ability, provided that this needs to be implemented.