Damnation feats get stronger as you select more of them, but they also give you more negatives (can't be resurrected, etc)
None of the abilities are added to the stats, or scale when you select additional damnation feats
I located the feats in data/pathfinder/paizo/player_companion/champions_of_corruption but they are just text descriptions with no bonus/mods at all.
I am still getting familiar with the LST format and don't really have any idea how to accomplish said task.
I am guessing a new Bonus variable needs to be added for "Number of damnation feats owned" and all of the bonuses and drawbacks need to be added to the individual feats.