I just did this last week. Changed from Jubilee to Mardi Gras one week later. Cost was $50 pp to change. Also if the cruise you switch to is more money you need to pay the new price. Just an FYI: there was just travel update for the Bahamas as well.
https://travel.state.gov/content/travel/en/traveladvisories/traveladvisories/the-bahamas-travel-advisory.html