In this hypothetical universe, is it as easy to change one's race as it is to change one's clothes? If so, it seems no different than "no shirt, no shoes, no service."

But then a world in which race was a choice would be so different from our own that one would wonder whether racial discrimination would even exist, or what "black" would even mean.

If I understand the arguments some folks are putting out these days, race, like gender, is now a social construct and therefore entirely mutable: https://www.nytimes.com/roomfordebate/2015/06/16/how-fluid-i...

I am not saying I agree or disagree with it, but perhaps things are not as hypothetical as you believe.