Actually, while I don’t know that “transracial” exists, that may be because “racial” is too big a category.
I think it’s possible that “transethnic” exists.
I know people who converted to Judaism as adults who are thoroughly immersed in Yiddishkheit, and by their speech or behavior, and indistinguishable from native Jews.
I know people who moved to other countries, and after several years, observe all the special celebrations of that country, have dropped or downplayed the ones of their native country, and have altered the way they celebrate shared holidays to be more like their new country-- they also have adapted their palates to the food of their new country; they speak the language, or dialect of their new country-- they may have an accent that belies their origin to an extent, but is not as pronounced as that of a visitor.
The same thing applies to people who change regions in the US, such as moving from small town Texas to downtown Brooklyn. Or a New England town to Hawaii.
Many people-- IME, more frequently, men-- have transethnic experiences when they marry women from very different backgrounds, because of a married couple, the woman usually does most of the work in holiday preparations, and such things, so traditions observed by nuclear families often default to the wife’s background.
Some people become fascinated by an ethnic background, and choose a transethnic experience.
I think this is a very real phenomenon, even if it isn’t recognized by psychology-- albeit, “culture shock” is, and so is “reverse culture shock,” although these are not really regarded as illnesses, just transitory states that are anxiety-inducing, and the person may need extra help and support getting through them; they’re like grief, or PTSD that way (some people have PTSD for life, though, and I never heard of culture shock emotionally crippling someone for life).
I wouldn’t be surprised if many people have gone to therapists with something like “I was born to parents of German and French descent, but I always felt like I should have been born into a big Irish family,” or “I’m obsessed with the idea that my not being being born Jewish was a cosmic mistake.”
I don’t know what a therapist would label that. Maybe an identity crises. If fantasies preoccupy the person to the point of disrupting their daily function, maybe DID. Maybe some kind of “obsessive disorder,” without the “compulsive.” I’m not a therapist, and can’t really guess.