Not easy, but managable if you use a mongo database 
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I did the same. I installed mongo 3.2 in an Ubuntu (virtual) environment. In my local development environment, I did not enable the mongo security setting. This allows me to do the database administration without authentication. Of course you should not do this in your productive environment!
Create your initial setup as documented. Configure everything according to your needs to the desired state before import.
Then shutdown nodebb and login to mongo:
use nodebb
db.copyDatabase("nodebb", "nodebb-backup-171003")
Now you have a copy, you can restore any time and can start testing your import tool.
To revert your changes, first shutdown nodebb and login to mongo:
use nodebb
db.dropDatabase()
use nodebb-backup-171003
db.copyDatabase("nodebb-backup-171003", "nodebb")
You can also switch between the copies of the nodebb databases easily by editing the file config.json.
Good luck!
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. Many thanks in advance!
. I will export the database of my forum and check what is stored there and do some code reading in the nodebb sources. I will come back to you, if I still have concerns after that.