Hey 506!
In my time playing the game, I have learned a lot in editor, but the one thing that I cannot seem to find anywhere is how to edit the call signs of your character slot template. (i.e. Instead of the first slot being Alpha 1-1, it's Delta 1-1 or something of the sort) I have placed the Zeus module for call signs, changed it to a custom one, then linked it to the corresponding soldier, but that soldier is still listed as Alpha 1-1 once the game is saved and played in multiplayer.