The most common thing I hear from a Bride and Groom after a wedding is "I wish we had done this/that"! Some couples wish they did things simpler and others wish that the cake was different, or the wedding was on a beach and the brides dress had been a colour instead of white. A Renewal of your Vows is a great chance to do things differently.
Personally, I would not tell anyone that it was happening. The invite would go out and it would be a shock to everyone. We would only have less than half of the guests that we had at our wedding, it would happen on the beach and my dress would be short and sweet. Oh, and a lolly bar would be available and I would ask everyone to wear the same colour.