You mean... documenting them?
Why?
Having a black actress play Anne Boleyn in a drama about Anne Boleyn's romancing of, marriage to, and beheading at the behest of Henry VIII - to which her race wasn't relevant - isn't the same as having a black actress play Anne Boleyn in a documentary about Anne Boleyn.
No-one's pretending, claiming, or rewriting history to state that Anne Boleyn was black - any more than they're pretending she was blonde (but white), big-breasted (but white), three foot two (but white), 38 years old (but white), when blonde, large-breasted, 38-year old little people play her in a drama.
Why is "black" the hangup for historical accuracy here?
It doesn't have to be black. Replace black with any other race, gender, or characteristic.
And I disagree. I see it as rewriting history when you change something fundamental about a historical character. That person never was a certain way, and there aren't any sources claiming they were a certain way, so why make something up or willingly change a known quantity? If you want to make the Queen of England black, then create a character who's the Queen of England and black, then put them into a series or movie. American media does it all the time with the president, and they constantly make up a fictional president for TV shows and movies.
I know you stated that it likely doesn't hold true on the opposite (unless I misunderstood), so given this line of logic, why couldn't Arnold Vosloo play Nelson Mandela in a drama series about South Africa? I mean, besides the fact that it's really culturally insensitive and would not sit well with people who thought apartheid was awful (for the record, I would not support Vosloo playing this part). If it doesn't work one way, it shouldn't work the other way.
Or you can do the latter while also allowing minority actors to get other jobs in drama as well, rather than limiting them to fiction, minor roles in Western dramas featuring real characters, or "a film about one of the many African empires" (which, given the nearest many black actors have got to Africa is their great-grandparents, is a tad condescending).
You brought up Ann Boleyn, who was the Queen of England in the 16th century, and we were talking about black actors. It seemed fitting to find something comparable around the same time frame, which is why I brought up media about African empires. It can be anything, though. There are numerous people throughout history that have stories worth telling from all races and cultures. But as I've said, if we're going to ignore race completely when it comes to casting actors, things are going to get messy, and I don't believe for a second that social media would look kindly on a white actor playing the role of a minority. There's already, supposedly, an uproar about the new Snow White movie and not having people with achondroplasia play the dwarfs. I'm not sure how widespread that is though, outside a few things that popped up on Twitter.
Again, why can a big-titted blonde play the character of someone who was a flat-chested brunette in real life, but a black woman can't play the character of someone who was a white woman in real life, in a drama? Why can we excuse every single physical characteristic except race when it comes to acting as a someone who was once alive in the real world?
A big-titted blonde shouldn't play the character of someone who was flat-chested and a brunette if it's based on a historical figure. I don't think we should excuse physical characteristics when attempting to represent a specific person. I think we can take more liberties when it comes to fictional works, although I'm not personally a fan of changing the source material when an accurate description of something is given. If you want to create your own story with your own characters, then do it.