u/_Gandalf_the_Ghey_ I can totally understand why that people might think that it was retconned and not traditional, but in this specific case it doesn't happen to be that way. I would honestly say that it is more like people are now re-embracing the mythology after a multi-decade period of rejection of it because of assimilation into mainstream American culture. You will definitely see some elders shunning people who identify as something other than "man" or "woman", especially if they are not fulfilling very traditional gender roles otherwise.

The genders like this have been recorded by non-native authors as early as the 1800s and is a part of the Diné creation myth that has been told for thousands of years! Plus, it isn't really a precise fit for modern western conceptions of gender - or especially of sexuality. For example, in traditional Navajo society (at least as I was taught, again), it is not acceptable to be a masculine gay man. If you are a person who forms romantic/sexual relationships with men, it is only okay if you are otherwise fulfilling a strict feminine role in Navajo society, and that is definitely out of step with modern American sensibilities of sexuality.

Plus Navajo hair is pretty difficult to dye blue in my experience. =P