This is Minecraft, but everywhere you go, the world constantly updates to replace the ores in the world with their block variants. The method which I used to do this was not worldgen tools, but constantly filling in the spaces occupied by ores with the ore blocks, and this was of course limited to 15 blocks either way in each axis of the player, as any larger area would be too large to fill.

I have a large project in mind, and it'll take me a month to finish. It's similar to the custom witch huts idea, but of a much larger scale