So, the old way of doing this with ETW/NTW doesn't seem to work anymore.
Firstly I removed the Shimazu, made playable the Shoni. When I launched the game, the Shimazu were unplayable (gone from the list), just like I set it, but the Shoni were not playable either. Just one less faction in the list.
A good thing to note is that the UI seems to adjust itself to make space for the clans that
are playable, so making more than the set amount per ESF may be possible
without luac or UI file editting.
Each of the factions seems to load a Variant file to be displayed as their 'unit', I'v yet to see the link to this Variant anywhere. It might be that the fact the unplayable factions don't have one set that is preventing them being playable even when set as playable in the ESF(?).
Furthermore I noticed something troubling, the Hattori clan are set as playable within the vanilla ESF, when using my Limited Edition Redeem code, nothing file wise seemed to change (barring perhaps the .exe) to actualy make them playable. So I don't know if this is an .exe limitation of the game to make certain factions playable? I hope not.
I'm waiting for Husserl to figure it all out atm.