There is no apparent reason for any conspirator to have faked Oswald's presence in Mexico City. It does not advance the plot to frame him from the JFK assassination but entails enormous risk since they would have to account for any witness who places Oswald elsewhere. In a conspiracy narrative, they would not fake pointless events like Oswald getting on a bus after the assassination that takes him nowhere. Events in a false narrative must have purpose. You don't see characters in a movie doing random things that have nothing to do with the plot. That is how a conspiracy plan would work. Oswald's defection to the USSR provides ample support that he was a Commie/Marxist. There is no apparent need to bolster that with a faked Mexico City visit if that is the alleged intent here.
The conspiracy claim (fasten your seat belt, here we go) is that the staged visit connects Oswald and the assassination he's framed for
back to the Soviets and/or Cubans. They were behind it and Oswald was acting on their behalf. This can then be used to either blame them for the act or can be used by the conspirators who faked the visit to stop the investigation into who the real assassins were, i.e., them, since the US would be fearful that it would lead to a war with Moscow. Yeah, I just repeat the claims I don't make them <g>.
But it's obvious to us that impersonating Oswald to connect him to the Soviets *and* then to the assassination two months later in Dallas is quite a plan. It's dizzying for me to imagine how you go from "A" - impersonating him at the two facilities in Mexico City in late September - to "B" - the actual assassination in late November. There are so many steps and paths, many uncontrollable, between "A" and "B" that you have to have a deep conspiracy view - one that thinks "they" have near limitless power - in order to connect them. You know the spiel: fake films, faked photos, planted evidence, coerced witnesses, and all of this covered up by multiple generations of Americans in the government and in the media for a half century plus. Gosh, that's dumb.
Back to my main point again: the Soviets *at that time* believed it was Oswald. They didn't think it *was* an impostor. This is not, as is claimed, something that Nechiporenko dreamed up in order to sell a book or curry favor with the West (note: he never defected, he stayed in Russia and worked for the FSB). Moscow had every incentive at that time and for the next four decades to expose this intrigue. But they didn't. Not then and not up to now.
Shorter: If you insist it was an impersonation then how to explain this? What, were they fooled too? Or were the Soviets working with the CIA too? How does this go?