Updating assets in general via CSV files is not yet possible. Using a database script you could do this. If you plan on going this way, you can consult the built-in report "Assets: Asset to asset relations" to find the database tables which are related to asset to asset relations.
Do make sure you create a backup of your installation before you start making database modifications, instructions can be found here: https://www.lansweeper.com/kb/94/backing-up-your-installation.html