You can use a dtoverlay to do a shutdown. It would be easier than your posted paperclip methode.
dtoverlay=gpio-shutdown will have Raspbian do a proper shut down when GPIO 3 is grounded. It can be set to use another GPIO of your choice though. For my fan shim I use the following
The fan shim button grounds GPIO 17 when pressed. Just change the 17 to the GPIO you want to use. Thats the BCM number not the actual physical pin number.
You just add the above line to the config.txt file.
The pinout for the pirate audio is here
I would avoid using any of the pins in use by it. Other than the ones used by the buttons that is. You could use one of those, you’ll just have to make sure their original function is disabled.
Just so you know, I don’t own a Pirate Audio, just one of the original Pirate Radio’s built around the phat beat.