When a creeper is about to explode the sound will be: "Creeper?"
And when it exploded: "Aw Man!"

How to control in game volume:

- Creeper? ---> Hostile Creatures

- Aw Man! ---> Blocks

 

Side effects of this resource pack:

- other explosions like end crystals and TNT will also have their sound changed 

- the explosion sound isn't perfect because minecraft randomly changes the sound pitch slightly (or something like that)