I recommend that you rethink the basic concept of what you are trying to do (which can't be done in a filemaker script anyway).
Using access privileges and scripts you can restrict a user's access only to records that they are entitled to browse and/or edit. Thus you can have a single set of user tables for all your users. If User A logs in with their password, they can only see the records from these tables that "belong" to User A. If User B logs in, User B can only see User B records and so forth.
This creates a system that should function the same as what you describe but does not require that a script create multiple databases with different file names and eliminates the update issues you describe.