There was mention of going via UFO to that other planet where they wielded Tridents, instead of Spears, so I think we can safely say that at least some items in the tribe-stage can be customized.
It doesn't seem implausible that fire pits and tents and all that could also be customized, just like in the Civ era you're making cosmetic changes to your city center but the game still knows how to interact with it because it's the same base structure.
Wasn't there a mention of the machine culture having glowing lights or whatzit on their buildings? That would suggest that you can place complex things, not just colors and shapes, on your custom content. So placing the particle emitter for a firepit isn't totally out of the question.
Huh, I wonder if the editor will need to have a system of checks on the editor to make sure content can't lag the crud out of people's systems if they make hyper-complex buildings or gigantic firepits that are spewing particles like a hose... but, Maxis didn't seem too shy about putting up lagtastic houses for Sims 2, such as a four-story bunker complex that could bring most any machine to its knees. The potential for content that could make performance suffer, might not even be a consideration.