From Total War Modding

(Disclaimer: Some of the opinions are solitary of Rhox's and might not align with the community's)

Startpos is turn 0 save of the campaign. The key point is, that there can be only one startpos. Thus, appending or removing via another mod isn't possible. That's why most of the users use only one startpos mod, Mixer. Technically, IEE and TOW are also startpos mods. But they're made to have each entry the same as Mixer and Chaos Robie's stuff are appended manually.

Due to this characteristic, Modders have made several works around for many startpos-only features, some parts are still startpos bound and need Mixer's work though.

Startpos things that can't be replicated

  • Cultures available agent_types: Mixer has added every possible case for every known culture and Mixer added culture. This would also mean the culture you added won't work due to this. Even if your faction does not have heroes, there is also the tech issue.
  • Slot types used for Landmarks: Same as above, Mixu makes slots for each region.
  • Potential for each faction: Same.
  • Factions: Both playable and spawnable need startpos work. Making it playable requires more work than just spawnable ones. Use the Mixer faction requests thread if you need them. Every playable entry increases the loading time so my advice is to practice with any mixer faction in it, then request when the work is complete. Also, Mixu prefers batch work rather than getting small requests multiple times
  • Diplomacy: For non-aggression and military access only. Others can be replicated via scripts.
    • cm:force_grant_military_access has some serious quirks and military access given by this can't be canceled in the UI
  • Regions held by a faction in the faction selection window: It needs startpos work but it's minor so I would say just ignore it
  • Faction leader CQI: If you need your leader to have a certain CQI, you need startpos. You don't normally need it unless you're going to make a quest battle for the leader. However, you can use a script to fool the users. Check Wh2 OvN's Halfing scripts

Startpos things that the script can theoretically replace but no one has done it yet

  • Offices: Because it's just an effect bundle given to a character and not so exciting for many of the makers. If you happen to make one, consider sending it to Mixu
  • Horde marker in the diplomacy panel: It's related to the feature forest, and the script below does not change this. Theoretically, you can change it with the script to change the icon and tooltip. (But I haven't tried)

Startpos things that can be replaced with script and DB way

  • Faction RoR (mercenaries): Setup mercenary DB and call cm:add_unit_to_faction_mercenary_pool()function at first tick callback new
  • Province mercenaries (raise dead and warbands): Similar but the function in the document is wrong so check other mods that use this function
  • Settings like starting region, leader, items, units, buildings, and such: Check other faction mods, Most of the things can be replicated with the script.
    • Faction starting position pin: Use frontend_faction_leaders_tables and alter the 'Override Force Location X & Y' column.
  • Tech node Set: While the tech node set is startpos, you can use some workaround. Do note that all the methods below need script work to lock all the vanilla techs you want to remove access from your faction. Otherwise, AI can research it plus will create research available alarm to the player when they have researched all available techs shown in the UI
    • Overriding some of the nodes with faction-specific nodes: Use the faction column in the node tables to override the vanilla one. Even CA uses this method for some of the factions. But it can only do overrides and the tech tree's shape needs to cover all the vanilla tech nodes.
    • Sending all existing techs to a place where users can't see: While you might not know it, every tech node set can have only one tech key. This means if you make a new faction-specific tech node that has a vanilla tech key, that faction will not have access to the vanilla tech node and will have access to the node the user has made. If you send all the vanilla nodes to a place with this method to a place where users can't see them, now you can create a new tech node set of your own. Check out OvN Dread King if you need an example. Note that it doesn't work for center-starting tech node sets like Chaos Warriors
    • Make a new tech tab and hide the previous one: Need some script work but also works. Do note that it can cause problems if another mod adds a tab of its own, but you can create compatibility if you want to.
  • Feature Forest: You don't normally use it, but if you're making a full horde faction (factions that can't occupy settlements) into a normal faction, or turning a full horde faction into a normal faction, but you can use other ways.
    • You can use the cm:add_or_remove_faction_features() function in the script to remove or add features from a certain faction
    • You can add more into feature into feature_set_to_faction_features_tables if you want to change accessible features of all the factions of that feature forest
  • Norsca vassal thing, and empire giving region thing (start_pos_entity_association_faction_regions_tables): Depends on what you're using it for, but since it's used in occupation options, you can use a script to hide certain things when the conditions don't match