1.11.2 How Do i replace Vanilla Blocks with the ones I created.

I found code that claims it can do this but it is for 1.7.10. So far i have this... I want to take the "fromBlock" and "fromBlock2" and have it instead generate my modded block. Does anyone know what to do?

@SubscribeEvent(priority=EventPriority.HIGHEST, receiveCanceled=true)
	public void onEvent(PopulateChunkEvent.Pre event)
	{
		
		 Chunk chunk = event.getWorld().getChunkFromChunkCoords(event.getChunkX(), event.getChunkZ());
		 Block fromBlock = Blocks.DIRT; 
		 MyModBlocks toBlock = MyModBlocks.MODDED_BLOCK;
		 Block fromBlock2 = Blocks.GRASS; 
		 

			 
			 //I want to replace Dirt and grass blocks with my modded Block
	}