You can use text commands via card to delete, overwrite or add any files to the device's internal memory. Also you can make a copy of individual files, folders or the entire contents of that internal memory back to a media card. Read this thread: [Only registered and activated users can see links. ]. You can put the XML in a Garmin folder on a FAT32 formatted USB drive to make a 'nuvi clone' and download any file your device is entitled to receive - that works for most older devices with GarminExpress.

As you're aware, some files such as detail maps and POIs work fine from a card. General rule of thumb is that files and folders which work from the device's internal .System folder will also work from a Garmin folder on a card but naming convention may vary. Other files however such as voice VPMs found in an internal root folder likely won't work from the card, but they can be added and removed by text commands as said above. Same applies to Text, Keyboard and Vehicle. Interestingly, in most devices GPI files don't even need to be in a POI folder on the card, they can be individually scattered around in the root and still found by the device. JCV files must be in a subfolder named JCV in the SD's Garmin folder for sure. Map IMG files can also be in a MAP folder and can be <any_name>.img, same as on the device's internal memory.