It works fine for me. Whenever I start the 767, it's cold and dark (the battery switch is OFF).

You could try reversing the way to do it. By that, I mean that you change the setting in the CDU (turn load default panel state ON), then copy the COLD AND DARK.cfg over to the custom folder.

I'm not having any problems with the EXEC switch working when I click on it.

Admittedly, I don't normally start the 767 using the COLD AND DARK setting, but the saved DEFAULT panel state that I created works fine. :-/