With this code no changes will occur to the block at the position

S23PacketBlockChange blockPacket = new S23PacketBlockChange(event.world, event.pos);
blockPacket.blockState = Blocks.diamond_block.getDefaultState();
playerMP.playerNetServerHandler.sendPacket(blockPacket);

 

however if i do world.setBlockState on the pos with the same blockstate var it will change to the diamond block

 

(Server only mod)

I am confused what you want. Do you want to send a package from the client to the server to make it change a block?

I want it to appear changed on the client, but not actually change it on the server world, so that i can show a area border when required.