MCStacker/tips/en/shulker_bullet.Owner.txt

The owner of the bullet can be set by entering the OwnerL or OwnerM (these are the owner's UUID's Least and Most). Alternatively you can enter the owner's coordinates. OwnerX, OwnerY and OwnerZ. If all five vales are set, MCStacker will ignore the OwnerX, OwnerY and OwnerZ values.