In windoze (XP) I have noted that if you plug in a Tom Tom, it appears as a disc drive. In the drive there are to be found numerous files and folders. I have copied the lot to my hard drive and then copied them back out to a new SD card. In my case the TomTom has worked perfectly on the new card. This new drive is larger than the TomTom original, so I have been able to add a fair number of new voices to the appropriate folder, more than could have been squeezed onto the original card.
The number of famous people who can now tell me to get lost on the TomTom is quite substantial!
P.P.