Things I have tried:
I have tried changing the XP of the units in Tavern, it changes but eventually revert to the old values after connecting. I assume this is because of the data being on the server-side? Even if I manage to fully level it, it won't allow me to change it's rank as the game will throw a connection error.
I cannot find the values on the arena, I wasted some medals some nada.
I was thinking of changing the values of the dailies, but no luck too..