Is it even possible to reduce the size of your penis and leave it fully functional?

Yes, but from what I do know of doing the practice, it's different than what you may be thinking. All I have to go by so far, to regulate size increase until I achieve perfect shape, is to use cold temperatures, where effective. My most favorite of such method is swimming in cold water, but my local community pool, property of the YMCA, has banned underwater swimming; and I didn't know until a lifeguard told me about it as I last did so--but that's a different story. The greatest part of the swimming method, is that proper shape manifests after a while.

You asked for it. I should say excite your partner before the real thing to avoid complain. Good Luck.