There doesn't appear to be a way to do this, but I wanted to check and make sure. Is there a way to change the volume of a sound being looped and/or before it's played? Currently, applying volume changes appears limited to having to start playing a sound.

SetSoundVolume(id,vol) would be a useful and important option.

Currently there is no way to reference a sound instance once it starts playing, for example multiple calls to PlaySound(1), will create multiple instances of sound 1, creating a SetSoundVolume() command would set the volume of all current instances. Is this what you intended?

Yes, adjusting the volume for all sound instances associated with a given index would be great. This would be useful for a looping sound effect for something approaching or going away from the player (ie breathing, engine noises, etc). If also possible, the ability to adjust the playback speed of the sound would also be beneficial (for developers interested in creating car games, this would give them the ability to provide appropriate revving engine sound effects).