You can now use a competitors mapping card to activate a Navionics Updates card for only $99. It does not require you do to anything to your existing mapping card, it only earmarks the card so that only one updates card can be used per existing card. So you will have 2 full functional mapping cards after activation.
Check more out here:http://www.navionics.com/en/navionics-updates
Also, check out the following video on the process:https://youtu.be/FiB9TJu9T6Q