The way I see it, there are two separate things at play in this claim. One is whether changa, or the mix, or the use of herbs infused with DMT and harmalas, in whatever form, was something that already existed before Palmer claimed he invented it. The answer to that is yes. That has been shown, and the proof is in the other threads the
@The Traveler mentioned.
The second claim is that he invented the name for this mix. That point is still disputed, but it seems unlikely. There are multiple people saying he did not invent the name, and only one person, Julian, saying he did. Given that imbalance, it makes the claim unlikely.
Taken together, this makes me think the conclusion currently leans toward Julian Palmer not having invented changa, but rather having spent his life building a marketing narrative around the idea that he did.
What I’m wondering is why the OP in this thread wants to know. If the goal is to change the Wikipedia page, that could actually be done fairly easily by showing that the cited “proof” is not really proof. The references ultimately trace back to statements by Julian Palmer himself, quoted or repeated by others, without independent verification. Because of that, there is effectively no solid evidence there. You could simply start an editing process and point this out, if you wanted to. Add the evidence about the smoking mixes and you have a fairly good chance.