If you want to change the Headshot sound for example follow these steps :
1.Make a copy of Emote_Alarm.cs
2.Change every Alarm in it to Headshot,don't forget the sound.
3.Go into Support_NewRewards.cs
4.Change this:
%killer.play2d(rewardSound);
(There are 2 of it,they are at the Headshot reward)
To this:
%killer.play2d(HeadShotSound);