Hi Lewis, I have had this issue before with other SCORM content.  As you mention you should only need to make sure the identifier in the new SCORM zip file match the old ones.

1. Extract the content of the old and the new SCORM packages
   
2. Open both old and new "imsmanifest.xml" files
3. Copy the "item identifier" from the old manifest to the new manifest, keeping the tracking data accordingly (first item of the old must match the first item of the new). Identifiers can be changed using a Text Editor such as Notepad - Take care of not breaking the XML e.g. by removing double quotes;
4. Save the changes
5. Re-zip all the new files, containing the updated  manifest file back into a zip file with the same folder and file structure as the original. (The manifest should be on the root of the zip).

Always test it before updating the live site!