Try this: rightclick and create a new text file, and save it as new.reg. Then paste and save the following text (between the lines):
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Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\\exefile\\shell\\open\\command]
@="\\"%1\\" %*"
"IsolatedCommand"="\\"%1\\" %*"

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The system should recognize it as a registry backup file. Double click on the file, and allow it to run (security permissions might be asked).

If you can't open notepad, try going to run (Windowskey+R), and typing "edit" and enter, and use that instead.