I can't quite imagine how a mod could help here. With a mod, you can change the probability of certain skills appearing for a specific hero class, but this probability doesn't depend on the hero's level.
That is, "arrows in the wheel." If you cut off all other paths, then this will be the only one! For example, you take Fire Lord, and after that, only Pyromancy is available, because the others are cut off or already depend on Pyromancy, and nothing else can be offered.
And it's changed not in the HeroClass.xdb file, but in the Skills.xdb file in the same folder.
