[Edi]

Zogundar, you can disable spells like Horror Mark, Curse, Doom and the one that gives several horror marks in a limited area by setting their research level as -1 or something, it takes them completely out of the game.

Then the only sources of curses and horror marks would be items and certain magical sites. The sites that do that are very rare compared to the total number of sites in the game and you unfortunately cannot mod out the curse/horror mark properties, but you can mod the entire sites out of the game by giving them a locmask of 0. For references, you need the Dom3 DBm which is linked in my sig, because I sure as hell don't remember them all, never mind the site numbers.