Save that Kodai's position was also probably suppose to be a higher rank (that of his brother's, a Lt. Commander). So he still needed to outrank Kato. (Sasumu was an Ensign rather than a cadet in Yamato 2199).
There might still be a need for certain qualifications before one gets some promotions. Though for all we know, Kato is the highest ranking pilot in the UNCF aside from the freshly promoted Kodai. (Kato would be a lieutenant, junior grade to Kodai's lieutenant in Naval terms)
I suspect that if Mamoru Kodai had made it back to Earth he's have been given a promotion to Commander (or possibly even Captain) and placed as Yamato's XO as well as Tactical Officer.
Oh and
Minori Chihara (plays
Celestera) added to the
Yamato Project group of singers.