Hello, and welcome to the community!
A good way to test whether this would work for you would be to do a full backup as your NSM currently exists (using dbadmin). After ensuring that your new backup is valid, try restoring the old backup to see if your custom signature sets are restored with it. I just did a test in my lab on NSM 18.104.22.168 and my custom signatures were restored properly.
Technical Support Engineer
McAfee. Part of Intel Security.