Same thing should work for those in the minor league player databases, such as ones who played only in the Negro Leagues, for example, as already stated with part two of the above instructions.
Say, for instance, you want someone like a young Satchel Paige in your game. In his case, you might go here to get his BB-Ref ID:
https://www.baseball-reference.com/r...d=paige-001ler.
If you'd want to import him as a 20-year-old player, you'd add the following line to your file:
paige-001ler,1927
If you'd want to assign him to a specific team upon import, you would then add the required team abbreviation after a comma that follows the season you'd wish to import him as being from.
This works for any number of players, as long as they have usable enough BB-Ref ID codes, even if they're only in the minor league database. Even if they only played in foreign leagues such as the ones in Japan, for example, it should still work. That's if you have the proper ID codes found and used in the text file you are using for mass importing of historical players into your desired league and/or desired draft pools, or free agency pools, or for adding to specific teams upon importing said players, of course.
Some players may have two different IDs on baseball-reference, one for their major league experience, and one for their non-major league experience as players. In that case, you can use either, I believe, to import players at whatever ages you choose for them to start play in your league at.
Hope all this information helps anyone looking for it, of course. And hopefully it's simple enough to understand here well enough somehow, too. If you have any more questions, feel free to ask others around the forums, like Spritze, for example, who might be able to explain things better to you folks here than I might be able to easily. CD out.