"HW rulez" mod (add-on) for HoMM3.

Question regarding M200. Solmyr, Dymir, and Aislin cannot use their signature spells without GM adjustments or other methods of obtaining the spell. However, the rules do not explicitly prohibit such a workaround of the hero-specific spell rule: a player can retrain the spell from these heroes and use it with other heroes. Is this a flaw in the rules and plugin, or is it permissible?