Adding Another Guest to Your Carnival Cruise Line Booking - 1 8oo--837~44~6o or 1 8oo--4o6~84~95 Travel plans can change before your cruise begins. If a family member, friend, or travel companion decides to join your vacation, you may be able to add another person to your Carnival Cruise Line reservation. Whether an additional guest can be added depends on cabin occupancy, availability, and your reservation terms. If you're planning to book a cruise or need Cruise Helpdesk Booking Support, reviewing your booking details before requesting any changes can help make the process easier.