Movie Magic Screenwriter - WINDOWS
Yes. However, the ability to add names only exists on the Windows version of Movie Magic Screenwriter.
While in the Name Bank (Tools > Name Bank), you can type in a name at the top, where it says "Find Name". If you hit Enter, and the name bank doesn't find the name, it will ask if you would like to add the name to your personal lists.
All the personal names that you add are stored in a file called Namebank.ini, which is located (by default) in the C:\Movie Magic Screenwriter folder. Make a backup of that file to save the names you have added, in case of a program or system problem.