The reason I ask this, and the reason it's not a dupe is because if we look at the answer to that question, we have, for example:
J.G. Hertzler: Appeared as three different Klingons (Martok, Kolos, and unnamed Commander)
Randy Ogleby: Appeared as the brothers Ah-Kel and Ro-Kel
Jeffrey Coombs: Appeared as two Ferengi (Krem and Brunt) and two humans (Mulkahey and Holosuite Guest)
Thomas Kopache: Appeared as two humans (Train Engineer and Enterprise-B Comm Officer)
Vaughan Armstrong: Appeared as three Klingons (Korris, Korath and unnnamed Klingon Captain), and two Cardassians (Danar and Seskal)
In addition, note that the same character appearing as multiple species is in bounds for this question but not the other one.
Which actor appeared on Star Trek as the most different species?
Now all the disambiguations. This is going to seem tedious, but otherwise we end up with a hundred comments/questions/debates.
Humans: we assume a character who appears as human is a human unless there's a good a reason to think they aren't (for example if they appear in the Delta quadrant)
Hybrids: A hybrid counts as each of its parent species, but not to exceed the number of characters represented. A single Klingon-human hybrid counts as one. If an actor appears as a human, a Klingon, and a Klingon-human hybrid, that is two, not three. This prevents the character in Enterprise's far-future mentioned as being a hybrid of a dozen races counting as a dozen.
Surgical alteration: counts. The character does appear as the other species. Farrell appears as a Bajoran. Sirtis appears as a Romulan.
Pure disguise: But if you just cover your distinctive parts, that doesn't count. Nimoy isn't appearing a human because he puts on a headband. (Aside from #2)
Other 'magic/powers/technobabble': counts. John de Lancie's Q appears as both a human and an android.
Borg: count as another species. Patrick Stewart appears as a human and a Borg.
Not played by actor: Janeway as a lizard does not count (thankfully!) because not played by Kate Mulgrew.
Voice work: Voice work doesn't count. This is like #7. The actor must appear on-screen.
Expect the list to get longer.