Here's a thread to help modders who want to make the following mods compatible with HGS:
- New lords and heroes
- New factions
- New spells, items, banners, traits, skills, and technologies

These will mainly be tables to be adjusted:
-ancillary_set_effect_junctions_tables
-ancillary_to_effects_tables
-character_skill_level_to_effects_junctions_tables
-effect_bundles_to_effects_junctions_tables
-special_ability_phase_stat_effects_tables
-trait_level_effects_tables

Assuming they balance their mods to vanilla values, you'll need to reduce all of the following effects by 50%:
- Replenishment
- Growth
- Movement range on the campaign map
- Charge bonus
- All forms of melee, ranged, explosive, and magical damage
- Leadership
- All forms of resistance (magical, physical, etc.)
- Melee attack
- Melee defense
- Speed
- Armor
- Stamina loss reduction
- Cooldown for all spells
- Wind of Magic cost
- Experience gain
- Chance to find magical items
- Ammunition
- Chance of defense and success of an ambush
- Points Life
-Unit mass
-Chance to block shots

Simply put, most of the effects that inflate stats are nerfed.

Everything related to the economy remains vanilla.

So browse the tables of the mod you want to make compatible and adjust everything related to these effects.

If you have any questions or doubts related to this, ask them here.