Most all travel insurance policies may be modified up to the day prior to your departure. Make sure that you request and receive revised policy documentation reflecting any requested changes.
To make changes to your policy, you must contact your travel insurance provider directly. If any additional premium is due at the time of the change, your provider will notify you and you can make the payment at that time. You are able to change your trip dates and your trip cost, up until the day before you leave for your trip.