Hi Tony,
The 'Export' function is incremental, but the 'Import' function is not. This means that the 'Import' will unconditionally overwrite a folder or file that already exists on the B2.
The way that I do 'selective' imports is to create a new 'b2Export' file on a USB device and drag and drop the music folders that I want to import onto that USB device.
Alternatively, if you have NAS enabled on the B2, you can drag and drop directly from your PC/Mac. This is very convenient, but works best if your B2 is hardwired to your router. It does work over a B2 WiFi connection but can be somewhat slow.
Regards,
Peter.