BEN said:
Quoting limited to 5 levels deep
You see, there are codes specified for official DLC.
The hacked DLC items take up codes and if Nintendo releases an item that will use that code, you cannot recieve that item.
Let's say the Blue Pikmin Hat (HDLC) took up the code that was meant for the Shamrock Hat. When you receive the Shamrock hat, the item will say Blue Pikmin Hat, and if you wear it, you will see a Blue Pikmin hat.
If you go to a friends town that isn't affected by this code, your friend will see you wearing a Shamrock hat while you will see yourself wearing a Blue Pikmin Hat.
People say it's safe because Nintendo uses tons of codes for DLC and there's only a small chance that it will take up a code of the HDLC. But it's not because there's no guarantee that Nintendo won't release a DLC that uses the code that the HDLC does.