Arthur Hlavaty has advanced in the theory (in the comments, in this previous blog entry) that Masks of the Illuminati's original title was The Devil's Masquerade. Arthur wrote, "One thing I noticed again is that the original title was probably The Devil's Masquerade, which I like. Presumably changed for commercial reasons." I asked Arthur if he could offer a citation, and he said, "That's a guess. There's the poem where each quatrain ends with the phrase, and it's an obvious theme in the discussion on the train."
Arthur's theory is attractive, because as he notes the phrase recurs in the novel. It also makes sense that the name might have been changed to remind readers that RAW is the "Illuminatus!" guy, although the Masks of the Illuminati title would seem to be hampered by the fact that the Illuminati are not very much in evidence this time. I like the alleged original title better, too.
Speculation is not proof of course, and it appears that proving that Masks originally had a different title is going to be difficult. I wrote to David G. Hartwell, the prominent science fiction editor who was the the editor for Masks of the Illuminati, and asked about Arthur's theory. Hartwell wrote back, "I don't know. But I would guess that Masks is the title Wilson put on it when he sent it in."
When I interviewed Hartwell about his interactions with Wilson, Hartwell didn't remember making a lot of changes to Wilson's books. Note the anecdote, by the way, about the time RAW met Philip K. Dick in Hartwell's hotel room.