Navionics and the rest of the companies advise you don't do this. There is potential to render the card useless. Then you're out $200, lol. Exporting them to a blank SD card is really easy, as is importing them into your new unit (Should find them automatically after it boots up).. One nice thing I like about the HB units, dual card slots.. One for the map, one for recordings, etc..
SD cards are cheap, I wouldn't take the chance.