Open your registry and for each key below change the value of "(Default)" to equal "Edit". This will change the default action so that the script will be loaded in Notepad.exe (or another specified text editor).
JS Files
[HKEY_CLASSES_ROOT\JSFile\Shell]
JSE Files
[HKEY_CLASSES_ROOT\JSEFile\Shell]
VBE Files
[HKEY_CLASSES_ROOT\VBEFile\Shell]
VBS Files
[HKEY_CLASSES_ROOT\VBSFile\Shell]
WSH Files
[HKEY_CLASSES_ROOT\WSHFile\Shell]
WSF Files
[HKEY_CLASSES_ROOT\WSFFile\Shell]
In addition you can change the default editor for each script type be changing the "(Default)" value under the [...\Shell\Edit\Command] sub-key.
Restart Windows for the change to take effect.