Can I run Spotify by pressing my F8 button instead of iTunes?
The simplest way to do this, is to set Spotify to Open at Login.
As long as iTunes is not opened, Spotify will get priority when you hit any of the special keys.

Alternatively you can install a little helper tool. Try these instructions from the Spotify Community Forum:

Download Bubo (https://github.com/jguice/mac-bt-headset-fix#beta-version) and move application to the Applications folder

Then go into your Mac System Preferences --> Users and Groups --> Login Items -->


Remove Itunes Helper
Add Bubo


Done!