I don't think that there's anything Rand can do. In terms of body chemistry, he is what he is. They say that Lincoln had a high pitched feminine voice, but that was before television. And, with Rand Paul, it's not just the voice. His mannerisms are also feminine.
Anybody can change if they want to.
Actors train for different roles, mannerisms, body language; vocalists are able to extend their range, and if you want to speak with a deeper voice, you go to a voice coach... that is all possible.
It’s all just a matter of being self aware.