The current function is mainly meant to dump all your data out if you want to stop using BandHelper, or if you want to copy your data into some other system.
If you want to import into another BandHelper account, you could rearrange the fields to make that work. It would be better to use the copy button on the song edit page in the app to copy a song from one account to another ... or if you want to share lots of songs, use one account with multiple projects, instead of multiple accounts, which eliminates the need to maintain separate copies of the shared songs.