If you use Identity Safe, before you uninstall NSS you will want to go into Settings > Identity Protection > Log into Identity Safe by clicking on Configure (if not already logged-in)
You will be interested in the Export Data option - you can click on Configure and will be permitted to browse your system for a location to save the data to. You can create an Identity Safe BU folder in my Documents or on your desktop - but the choice of location is yours. Select a location you will remember.
IMPORTIdentity Safe Data.
Once NSS is installed, go back to the Identity Protection Settings page (above) and Select Import Data by clicking configure. If you set a password when you saved the data, enter that password, the location of where you saved the data and then click OK. Your Identity Safe data should be restored to what you had before you uninstalled Norton.