If a non-Jew [ex-Muslim] is working with the Beit Din for an Orthodox Conversion to Judaism, is he still considered to be a Noahide as he does not yet have a status of being Jewish?
Even in the most extreme case of death, prior to completing conversion, the candidate remains a Gentile.
The candidate today could be called Gentile or Noahide. I distinguish the terms, as do a lot of Noahides, but I don't actually think it makes any difference in Jewish law about the term. I'm unsure a candidate for conversion would refer to himself distinctly as a Noahide, though that might be technically correct. Usually, the term is for people who are living as Noahides. If Gentile who has never heard of a Noahide went to a rabbi who has never met a Noahide and asks to convert, I doubt the term would come up at all. As unflattering as it might sound, until you are a 'yid,' you are still a 'goy.'
However, I suspect that if Jewish law has historically called people who were in the conversion process "Noahides," a lot more Jews would know what a Noahide was by now.