EPPM: Updating Resources using Spreadsheet

I have successfully loaded resources using the Import from Spreadsheet option in the Web.  Quite simple, actually: Create a template, populate it and pull it in.

Unfortunately, when the resource already exists, I get a "Unique Constraint" error.

• Row 3: Failed to set value for UDF_302 because Failed to set value for UDF_302
• Failed to create resource George Jetson: Errors located: Resource ID: Unique constraint (Resource ID) violated. The value 123456 of the field Resource ID already exists.

Should I be able to do an update in the web?  It works in the Client version.