Currently, we don't have a method of doing so. And since Konashion made SDT without releasing an .fla online, it would be difficult to change something in the game that is pretty much inaccessible to normal users, and a pain to programmers, seeing that the game cannot be decompiled and recompiled properly.
BUT, we have made progress adding sounds that don't overwrite old sounds, so it can't be that far off to change such things. I personally wanted to be able to adust Her breathing sound level, since right from the start, Her seems to breathe quite audibly. I suppose the Cum sound effect sounds a bit too ridiculous as well.