Again, I don’t think you’re quite understanding how absurdly vague the civ is - it’s not like being able to call India the Mughals or renaming Germany into Prussia - it’s like having the Swedes so ridiculously vague that you could rename them to the Russians and the civ would be just as accurate.
The Cheyenne and Mandan aren’t part of the Seven Fires - the Mandan were enemies of the Seven Fires for a long while, and the Cheyenne speak an entirely different language, but you could rename the Lakota into either of those civs and it would be entirely as accurate. The entire foundation of Cheyenne culture is different from Lakota culture - the differences between the two should be astronomical in proportions. The two nations may have been allies, but they were about as alike as the Portuguese are to the Russians.
There are only two distinct features in the entire civ that even so much as hint towards it being Lakota, and one of them isn’t even Lakota, it’s just something that happens to be associated with the Lakota due to what was likely a translation error. The other is just the name of a unit.