Yes, the export/change/import can work. There are a couple of things to be aware of before starting. First make a back up of your current file, just in case. Second do not change the format of the file. All changes to the data must conform to the protocols set out for the import to work. Definitely do not change the first line of the export file as it is already set for the import to work best with your data. When you try the import after making the changes a log will be prepared. Check the log thoroughly as any errors to specific records will be noted and you will have to correct them and make the changes manually (if only a few) or do another import with the corrected file.

It can work - it will work! 

Clyde,

The export of a customer list, change and import into a NEW file will work but only for most of the info on the Address tab of the ledger.

If a customer name exists in the file, an import of a customer with the same name will not update any other information.

The only way to do what BrendanG wants is to do a custom import using tools not in Sage 50.