Ok. Well consider the following points:
1) In the <Type> tag, it's probably easiest to call them with the number as in: TRAIT_AGGRESSIVE1, TRAIT_AGGRESSIVE2, TRAIT_AGGRESSIVE3 and TRAIT_AGGRESSIVE4.
2) Then the Description text reference calls them Slightly Aggressive, Moderately Aggressive etc...
3) PromotionLine needs to all have the same reference in a given set, so all Aggressives would have PROMOTIONLINE_AGGRESSIVE.
4) iLinePriorities need to count up. Thus, the non-Developing Leader version is 0, the first step such as Slightly Aggressive would be iLinePriority 1, then the next step, Moderately Aggressive would be iLinePriority 2 and so on. The NEGATIVE traits count the opposite way, -1 on the first step into Developing Leader versions and continuing into -2, then -3 etc...
5) As for text files, I'd start one of my own if I were you, just to keep them all where you can easily find them. Copy any existing text file (you can use mine) in the Assets/XML/Text folder, rename it, then go in and remove all text reference entries except the first. Then overwrite the texts within the language brackets (make sure to put all the non-english ones in english so that the translators know to address those) with what you want the reference to say in the game.
You can probably find the text references already established for a new trait, like Progressist, somewhere in our text files for an example of the wording. Just having a correctly formatted text reference located under ANY file name but within the Text Folder is enough for the game to connect the tag call in the trait to the text reference. It's a very clever and simple mechanism.
6) The Impure has two tags, ImpurePromotions and ImpureProperties. If a positive trait has a negative promotion or a negative trait has a positive promotion then the impure promotions tag should be set to 1, otherwise 0. If a positive trait has a negative influence from property manipulators, or a negative trait has a positive influence from property manipulators, the impure properties tag should be set to 1, otherwise 0.
7) For now, I suggest just keeping the flavors set to the same as the line's predecessors, just duplicate them as is to the new tiers. I'll give them a better smoothing over afterwards.
Any more questions?