Export the customers to a csv file with the columns/fields you need. Make your changes and import the file again. A test data base would be good to check if it works.

The first column contains the ids of the customers. You mustn't change the ids. And don't add new rows to the file. Then the existing customers should be updated only when you import the file again.

Hello,

I see 2 solutions : 

- You create a unique constraint in your postgre database to make the name unique

- You take the id generated while exporting and you put it in id column while import.

Regards,