There has been much ado about Rachel Dolezal, a woman who tried to pass as black or African-American, and became the head of the Spokane NAACP before resigning when her parents revealed she was of overwhelmingly European heritage.
But setting aside her specific case, why is it hard to imagine people switching their racial affiliation when they commonly switch religious or "tribal" affiliations all the time? People who become Jews, for example, cut off ties not only to their ancestral religion, but also their ancestral heritage. Is it really that different to change one's racial affiliation?
It is hard to put specific cases aside because they provide context. But, I imagine we could come with some contrived circumstances that make it okay. But I will try to proceed by contrasting the idea of changing racial categories with changing other categories.
One of the most common contrasts which are brought up are change of race vs. Change of sex. Change of sex is usually pursued by those who identify as the opposite sex. This is most often described as a life long identification combined with a feeling that one is in the wrong body. As has been pointed out race is a social construct. This in itself is a hotly debated subject, but whichever side one falls on the discussion, we can agree that just because something is a social construct does not mean that it is not real, perceived, and has impact. While we could point to gender identity as a social construct, this too has differences from race as a construct. And, while changing gender constructs could in theory diminish the want for sex change, this construct is rooted in differences of masculinity and femininity assigned by society. Racial differences, by contrast are almost strictly phenotypic. While we have assorted stereotypes in our society, most stereotypes are negative. And the stereotypes which are not negative are acceptable for other races to possess. Given all of this it is hard to imagine someone since their very early ages, believing they were of the wrong race.
Religious identification is different too. Religious affiliation is based on beliefs. Nothing in racial categorization is dependent on beliefs.
Tribal affiliation too differs. Tribal affiliation is based in the group with whom you associate and of whom you are considered a part. We can find instances of tribes taking in outsiders the outsider and subsequent generations becoming part of that tribe. However, there is no tribal affiliation with racial categorization. Race is based on phenotypic expression.
Given this, one is left to wonder why another would change race. The answer seems to be almost exclusively deception. In other words, to find acceptance based on appropriating historical achievement and adversity and creating the illusion of shared experience. For, however right or wrong this has become the significance of race. Many see race as an identifier of experiences common to those whom possess certain phenotypic attributes. What purpose other than for deception would one want to have this association?