I have plans for putting together a mod based on the Epoch setting from FantasyCraft, a setting that takes place in a sort of mythic stone-age where primitive tribes do savage war with an invading empire and its demonic powers themed on the Aztecs, called the Keepers of the Gate. But there's a few things I need to sort out.
1. I can restrict access to metals just by stripping the normal ore code out of ores and giving custom metalworking reactions to turn those stones into metal bars only to the aforementioned Keepers, right?
2. Having done that, I intend to expand the ability for various tools to be made out of stone (as well as adding a couple more stones useful as weapons and a workshop to shape these stone tools and weapons). Is there any way to ensure that camps are able to start with these stone tools, so that they'll have consistent access to axes and picks and such? Also, are there any material requirements that a material has to meet to be valid for chopping down trees/mining now that training axes no longer can cut down trees?
3. The Keeper society is explicitly one in which humans and the demons of the setting, ghula, exist side by side (though with the Ghula as leaders), and the Keepers have priests who use secret magic to bring the powers of demons into the world. Is there any way to a. ensure Ghula join the society as rulers (I know I can give them the tag that lets them take over a civ as a Power) and b. ensure that a specific caste of the Keepers receives the Secret of Ghula Magic?
Good luck! Always been vaguely interested in a primitive world mod, but not quite enough to actually do the work myself.
Anyway, 1) Yes! I routinely do that just to better fine-tune metal access and smelter reactions. You lose the ore indicator in the embark screen, but that's no huge sacrifice.
Then you use custom reactions to add metals to civs, like righthandoftyr said.
To affect playable civ(s), leave the reaction name blank and add it to something obscure (e.g. soap maker). You'll never even notice during normal play, and it provides a handy free-resource cheat if you want to test something on the fly later on.
(Side note, you can also remove metal access by disabling the Furnace Operator labour from a civ)
2) That's... harder. DF really isn't coded with stone equipment in mind - everything is made from metal with only a few exceptions. Even randomly-genned bows and shields are all metal.
If you're going for a true stone-age world, then the best compromise by far is to tag all work stones (maybe even all stone full stop) as the new 'metals'.
It's not a perfect option - they'd be automatically smeltable and forgeable, if you chose to build those buildings. But in general it'll give the behaviour you want with minimum headaches.
Embark/traded axes and picks are always metallic - a reason for the above workaround.
Training axes can't chop trees because they lack an EDGE attack. Material (as usual) is completely irrelevant - a hatchet made of wax could chop down an oak tree.
3a) Getting way more complicated. Never really experimented with this stuff myself, but as I understand it:
Maybe you could make them DARK FORTRESS civs (which are explicitly founded by escaped demons).
Maaaybe you could set randomly-genned demons to zero, so that only Ghula remain in hell? Logically, only they could escape to found new Dark Tower civs.
You'd have to accept that your Keepers live in Goblinesque towers made of hell-rock, and have exactly one genuine demon per civ (the initial founder).
To my knowledge, there's no way to make demons reliably take over non-dark-tower civs.
3b) Bit hazy on what 'the secret of Ghula Magic' is actually supposed to do. Assuming you mean summoning more of them?
All I know about summoning interactions is that most are absolute bastards. Search around, you'll turn up options, but they're hard to implement and hacky as hell.
You could maaaybe make a priest/summoner caste with a transforming reanimation interaction (ala necromancers) that turn corpses into Ghula. Use a ridiculous cooldown to prevent them from using it outside of worldgen. But then you'd be getting hordes of subservient Ghula per priest, which doesn't sound like what you're after at all.
Honestly? Think the most elegant (and easiest!) option might be to just copy-paste Ghula as a rare caste of Keeper. High natural skills would help them reliably rise to leadership, and of course serve as challenging enemies.
Sure, the Legends would record Keepers marrying and/or giving birth to demons... but that means you'll be leading a bunch of hopelessly outgunned stone-age tribesmen in eternal war against literal demon-fuckers, which sounds pretty metal/dwarfy to me.
In fact...