Careful, it's very easy to get two different people with the same first and last names.
You can do what you describe with import records, you can select two options for the same import: "update existing records in found set" and "add remaining data as new records'.
You'd want to show all records before importing. If you use a script for this, be careful to update the import script each time you change table definitions by adding/removing fields unless you are able to import using the "matching names" option for your field mapping. (And you still may need to update to add a new pair of fields to the order.)
Finally, make a back up copy before doing this for the first time so you can toss your files and try again if you don't like the results.
Another option is to set up a looping script that does this one field at a time.