NO. Issaggans are staying Saguan. You know why?
Just because the Issaggans have a different culture from the Saguans doesn't mean they should be a separate species. Look at Earth for example. There's cultures from Bantu to Maori to Portuguese. All these cultures consist of humans.
Or, if you want them a different species because of coloring, look at domestic cats and also people. People are varied on a scale from almost black to very nearly white, and we're one species, are we not? Cats can have all sorts of patterns from calico to pure black to tabby, and they're one species.