You'd have been better off to backup the file before editing then you would only have to overwrite the edited version.
In the appearance tab change to any other blind (not Longhorn 5203) and exit the display properties. Use Windows Explorer to navigate to the Stardock\object desktop\windowblinds directory and delete the entire Longhorn 5203 directory and any others that are empty windowblind directories. If it returns a message saying it's in use you may have to reboot. Then download the wba file from here and double click on it or choose run when you download it.