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It seems that you are using Windows to modify backup file, please try to use Linux, you can use VM to install Linux on Windows computer.
Here’s the link to download Ubuntu 16.04 OS http://releases.ubuntu.com/trusty/
Using Linux, you can simply open backup file, change the continent of it and save, then upload the backup file back to the router after moving it to windows again.
Should you need any additional information please let us know.