You must use Garmin reverse converter with Garmin NT maps to convert them in non NT maps to use them on old devices and to unlock them
Run the map converter ,move the All.bat and GarminUnlocker.exe inside that folder with all the maps that must be converted to img format and run the All.bat
Your maps will now be unlocked . Uninstall the maps using the add remove in Windows control panel. Once the maps are uninstalled, MapSource will find your maps.
Now you can send the map to your gps device
To split and merge maps use GMapTool