Steven Zahm@ Richard
Navigate to the Connections : Tools admin page, click the Export tab, scroll to the bottom and use the Export All tool. Open the CSV file in LibreOffice Calc or Google Spreadsheets (avoid Excel) fill in the logo URL for each entry. You could get crafty and use a formula to take the base URL and filename and concatenate them together so you only need to enter the base URL once and add the filename for each.
With the latest release of the CSV Import you can import the logo by importing your updated CSV file which has a fully qualifies URL for the logo.
The only thing that could throw a wrench into the works is… do you have any of the repeatable fields, such as the address and phone field sets, where you have more than one of the same type? For example two addresses for an entry with their type both set as “Work”? If you do, only one of a type will be exported so when you update you will lose one of the “Work” addresses. Hope that make sense!
Hope this helps, let me know.