So, basicly these DLC datapacks change/reset everything you edited in fake, blank leagues? Like when you create Bundesliga over PAS league. And also it resets all the fake National Team players names to default? I hope that is all.
What else should we know, does it affect edited kits, faces, club team/player names, manager names, chants, stadiums, banners?
As I understand the solution for blank leagues is that your export created teams and after DLC you can import them back, but cant figure any solution for NT fakes, as you would have to start everything from zero again. I also have created some players and assigned them to teams where needed. I guess they will disappear, since DLC updates transfers as well. There is so much time and work that needs to be put in order to edit your OF`s, so you try to be as much cautious as possible.