There are 2 places for this to change.
Game folder have some archives in which are units files placed. Game folder/sessions/addon/data.kfs and ses.kfs , look for .atom files. For example all old units are in data.kfs like : footman.atom(this is swordman) and footman2.atom(this is guardsman), elf.atom and elf2.atom(this is hunter) . And all new units are located in ses.kfs like all viking race units yotun and other units new in WotN.
Look around there a bit and you should find all files you want.
Open archive with wnzip/winrar then some of those atom files open with notepad/wordpad and in
leadership=XXX , change XXX to your choice. Save file, close it, and close archive after that. New lds cost should be listed in game, no need to start new play.
Good luck
