Can you have a belly button piercing in the Air Force?

"Members are prohibited from attaching, affixing or displaying objects, articles, jewelry or ornamentation to or through the ear, nose, tongue, or any exposed body part (includes visible through the uniform). EXCEPTION: Women are authorized to wear one small spherical, conservative, diamond, gold, white pearl, or silver pierced, or clip earring per earlobe and the earring worn in each earlobe must match. Earring should fit tightly without extending below the earlobe. (EXCEPTION: Connecting band on clip earrings.)"

So basically, whether you're on or off duty, you can't have a piercing or tat that shows. From what I can tell you could keep your belly button piercing- EXCEPT they might make you take it out for boot camp... they're really strict there...
but if you wanted to get it pierced, or re-pierced after then you should be good :)