Changing the folder to the device's correct HWID and its GarminDevice.xml is not sufficient. It's essential the other device's correct boot.bin/ldr.bin (ramloader) from the other firmware is also used. That's because if you flash the wrong ramloader you'll likely hard-brick it irretrievably, that includes a device which previously had its USB connections working. The ramloader is flashed to a virtual region (rgn12 - hex 0x0C) and it in turn writes to regions 5 & 43 on the next attempted boot-up. The bootloader in rgn5 is like the BIOS of a PC, screw that up and there's no boot possible. Be aware that even if a device that's lost USB connectivity becomes 'soft-bricked' due to a faulty file or corrupt firmware, that there is no way back. That's because the ability to read a media card is dependant on a device at least partially booting. If it can't get far enough into the boot process to look for the card that there is no way to fix it if it also hasn't got preboot available.

So be absolutely sure you understand this stuff before going further. The only protection against any inappropriate SD flashing is the naming of the HWID folder. If that matches the actual HWID of the target device it will accept the flash, doesn't matter whether any of the files on the card are or aren't correct for the device.

BTW, not all devices have every one of the possible SD commands written into their firmware, but you can check using a Hex Reader which ones are present. Only devices with a visible file system will have the ability to use a media card in this way, very old 'region-only' devices like early StreetPilot models operate quite differently.