[VanillaGorilla]

Bru's question spawned what I believe is the answer to the OP's question.

In League Setup you can scroll down on the right hand column and select 'Randomize Player Names.'

If you turn off recalc, you have, in effect, a group of fictional players that represent the historical ethnicity of MLB.

So, Jackie Robinson will debut in 1947, but as a different name. You could always create a player to break the color barrier prior to Robinson, if you wanted to do that, also.

I have not done this with the idea of replicating ethnicity, but I did not notice any randomization of ethnicities when I randomized the names. I am 99% sure that this will give you something similar to what it is you are wanting to do.

ADD: I just did the randomization of names as a one time thing. I did not play multiple seasons. I do not know if the historical draft pools will import with randomized names, or not, after you perform the initial randomization. Sorry, my suggestion was not as solid as I thought it was.