Couple of questions:
1. Did you load the standard database down to Conference North/South, or did you load one of those 'English Leagues down to Level 10' database files?
2. If you loaded a custom lvl 10 database, did you edit and create the chairman on that file or did you create him on the standard database?
I think, could be wrong as I've not tried this yet, that if you create a non player on the standard database and they are below the playable leagues selected, the game will generate new staff members for the team when they become playable, especially if you have 'add key staff' ticked in the game setup.
If that is true then the only way around it will be to edit him onto a 'down to level 10 ' database and load that when you start the game. I know that kind of defeats the purpose of the challenge but it might be the only workaround.