Call and make a PS with Disney Dining. 99 times out of 100, the CM taking the reservation will have NO CLUE what you are talking about. That's OK! Ask them to note on your PS "Rehitching Ceremony" or better yet "Wants to do Rehitching Ceremony." The CM doing the reservation can make all kinds of notes, so be sure to ask for that.
When you arrive and check-in, TELL the CM on duty that you want to do the Rehitching Ceremony. Sometimes the CM may not notice the note and on rare occasions, the note was not there. The CM on duty will wrtie this on your card. When I did this, I watched the CM write it on the card -- just to be sure.