Custom stone generation in overworld

[fallOut015]

In my mod I want it so that in deserts all stone (or just stone in certain y values) is replaced with sandstone. At first I tried looking at the overworld generation class, then I tried ChunkEvent.Load, but these didn't really seem to help (ChunkEvent.Load worked at first, but it would also replace stone blocks I placed and it wouldn't save the blockstates to the chunk (I think? when i interacted with the sandstone it turned back into regular stone))

What's the best way to go about this? I looked into the ore generation features and replacing stone with sandstone, but I'm not sure which configurations to use. 

(Preferably this would happen at world gen or chunk generation when the stone is created)

[vemerion]

You could create a new class that extends net.minecraft.world.gen.feature.Feature, and add that feature to the desert biome. Try looking at the vanilla code features to learn more about them.