Hello there!
We would recommend using your database cleanup options as per usual, so your scanned assets are still cleaned up and then excluding the manually created assets from being cleaned up.
You can prevent specific assets from being deleted or having their state changed by your cleanup options. To do this, click the Assets link at the top of the console, tick the checkboxes in front of your manually created assets, hit the Mass Edit Assets button on the left, and tick the Not Affected By Cleanup Options field.
This is also explained here: https://www.lansweeper.com/knowledgebase/performing-automated-database-cleanups/