take the completed form DS230 to the embassy before your interview date cos your file is already there, i am positive about that.
thanks
But this what they told me after sending a mailto the embassy.
For Diversity Visa entries, if you are inquiring about adding a family member (that was NOT a family member at the time of your Diversity Visa entry) to your DV case, it can be done on the day of your interview at the U.S. Consulate. All normal DV fees apply for this family member.