You can replace only the handle without removing the whole parking brake assembly. First you remover the button at the end of the handle. This takes a bit of force and a good grip on it, which is really the only thing that makes it a little bit difficult. Once the button is removed, gently but firmly twist the handle back and forth while pushing it off. Once the leather handle is off, slide the carbon fiber handle on and replace the button.
I did this in my Boxster and it took about 5 minutes.