So far I was unable to add new ranks, only replace the current ones which I suppose is no big deal. But, I'll post what I've changed/found out and maybe someone else will figure it out.
The two files I've edited are the "career" (program/scripts) and the "common" file (resource/ini/texts/english)
Career[0].rank = "Sergeant"; <----rank
Career[0].pirate = "Vagrant"; <---pirate rank
Career[0].points = 0; <-----determines how many missions you must complete before promotion
Career[0].money = 500; <-----monthly salary
By only changing the rank, in-game you'll see a blank space, no reason why from what I've seen, so atm, you can not edit the ranks in the "career" file, but thats where the "common" file comes in.
string = Sergeant,"Sergeant"
string = Lieutenant,"Lieutenant" <-----these can be edited, the stuff between the ""
string = Captain,"Captain"
So say you want to edit the Liutenant rank to Ensign you edit this in the "common" file and in-game you'll get ensign instead of a blank space.
But, if you try to add new ranks in the "career" file, when you reach that rank, you'll get a blank space in-game.