If you manage to check the Spreadsheets file for the game, it already shows a fourth military trait known as Aptitude, which I think is supposed to determine how well your military increases experience. Currently, I'm trying to find a way for the Aptitude trait choices to appear when I customize a race right before a game.
TimeTraveler: I think you just need to move the entry for Aptitude back in to the main table of racepicks. It's the third table. Aptitude has been cut and pasted after the end of the table; you should be able to return it to the game by cut & pasting it back in a new line after the Accuracy entry. (Whether the modifiers in the Aptitude table have an effect any more, I don't know, but this will at least put it on the race picks screen. )