About changes and/or combining Hero Specializations.

I understand that scripts will only work within a single map, not the entire game, right?

But if we're talking about the version with scripts, it would be good to have more details. This could be useful for one of my projects, to create more interesting Hero Bosses, without being limited to campaign-specific overpowered abilities.

I think you should check out the NHF project, and if possible, contact its authors. There, special abilities are distributed not only to one map, but also to many others. And there are some very complex special abilities that I'm not even sure can be implemented with standard scripts. As has already been noted, without an executable file, special abilities will be limited to the boundaries of a single map.