Whenever I try to import .episerverdata exports that I've tampered with, the import fails. Or rather, it succeeds with zero files found inside the package.
I renamed the .episerverdata file to .zip. Then I extracted its contents using 7-zip. Without making any changes, I zipped it back up using 7-zip, renamed it to .episerverdata and tried importing.
The untampered .episerverdata imports as expected.
Am I doing it wrong?
I found the answer. The re-packing had resulted in the files being placed inside a folder in the .zip file.