That's a good idea!
Instead of sharing it, i'll post a brief tutorial with most of the steps to follow.
1 - Download CM Explorer
here
2 - Create a save game with the leagues you want and pick the weakest team or even one that has no manager.
3 - Save it and exit after.
4 - Run CM Explorer as administrator and load your save game at "File". Make sure you select "Saved Game .sav" and not "CM Database .index data" at the option below. You might need to go a folder level up and return again to your game folder in order to find your save game.
5 - Double click at CM Database, and at Staff you can you the option Find located at the binoculars.
6 - Double click your name and you'll open your stats. In this case i've made Hallescher's manager. Now you can pick any team and if wanted a national job at any country (under21 included). After those selections you select ok, and save it at "File".
And this is pretty much it. Only takes a minute or two.
