Oh you have to use a patcher :/ you wouldnt happen to know what the limitations are by chance would you?
Basically that you can add, but not replace or change older data.
When playing, some data is copied into the savegame and some data is loaded from the original data. Changing the original data will not change everything that was placed into the savegame - that's why you have to start a new game when you add certain scripts or make changes in some database areas, because those changes would not affect the savegame.
The same problem appears when you try to apply those changes as patches after the game was distributed - using an old savegame can then break the game.
If you force the player to start a new game for the changes of the patch, most things usually work - but that's usually not what's intended by added content...