I don't think you understand. Nitrogen doesn't touch those things. The only thing it does with biomes is draws a picture, that the game then uses to read ITS biomes.xml (where those things you're talking about come from) to generate them.
So no. Since the program doesn't do /anything/ with said decorations, only prefabs, it doesn't have any hidden features to change them.
This is the case in both rwg AND nitrogen. Both generate the world prior to reading the other xmls.
Height, roads, water, prefabs and biome /type/, not plants, weather, decor prefabs, loot blocks, etc... That's all handled in biomes.xml in both instances, unaffected by the system that creates the world itself.
There is no modlet that loads before world generation.