Does exactly what it says on the tin, replaces the Ultimate Combat headshot sound with the satisfying headshot sound from Halo 5 Guardians. 

Known Issue(?):

The Ultimate Combat sound used for headshots is also used for parries, so you'll also hear this noise for parries which may or may not sound as cohesive. I personally don't use the timed block/parry from Ultimate Combat, so I couldn't tell you if it sounds as good for parries as it does for headshots.

Preview (0:15 - 0:20):


Dropbox preview (the actual sound used) and source: here
Actual guy's comment (the guy who extracted the sound, C1eric): here