I like your mod a lot (you might be able to tell) and the cave layout is always the same. I'm trying to figure it out but there's some questionable things, like in chunk_generated for caves, local path is assigned but I don't think it's used, unless it's found by a surface.function. Water is always in the same place, as well as resources (though what resource it is is random - and only vanilla resources because they're explicitly generated, not taken from data.raw.resources or autoplace controls). I'd like to make a bunch of changes (and I am for my local copy) but with no license it is frustrating and probably illegal.

yes I know, it's not my mod though, Give credit to Decu, and I haven't played Factorio, I'm busy in real life, but I appreciate your posts. I wouldn't worry about the licence. Go to your save file, folder maps, cave, surfaces, cave.lua and on line 14 you have Noise.seed(555319). Change it to whatever seed you want, I think that should change it. There's some mod around that regenerate chunks in case you want it changed early, I never tried the mod. You can also confirm this by downloading the aircraft mod and creative mod to use cheats, drive an aircraft and throw a bunch of atomic bombs around to destroy the rocks. Note that the only thing that changes on the SAME seed, is the type of resource. One time it might be iron, next time might be copper etc. Cave shapes, resource shapes, water shapes remain the same on the same seed.

Hope that helped.

That helps a lot actually. I tried out something else and it didn't work.