Another approach:

Press F6 to bring up the SmartFinder. Edit the columns to select Customer number, name and salesman code. Create a filter to select only the records with the old code. Send the resulting Grid to Excel. Change the salesman code in Excel and save the sheet. Define an import template naming the Excel sheet and containing the fields Customer number, name and salesperson. Turn off the "Add records" option. Import the new salesperson. Run the SmartFinder again to make sure all the records have been changed.

You would have seen this done at the AOC! (Thanks to all who took the time to make the trip.) I hope we'll see you next year.