1. Open Registry Editor
2. Browse down to HKEY_CLASSES_ROOT\*\shell
3. Right-click on “shell” and choose to create a new key, calling it “Open in Notepad”.
4. Create a new key below that one called “command”.
5. Double-click on the (Default) value in the right-hand pane and enter in the following:
notepad.exe %1
6. Close Registry Editor
The change should be immediate.
You can do this with any other favorite editor, just make sure the executable is in your path, or specify the full path in the Default value i.e. c:\program files\myfaveeditor\editor.exe