While you can't make a lip piercing completely invisible, you can hide it pretty well if necessary while you're at school or work. While a Band-Aid will draw attention to your lip, and it will most likely be clear that you're covering up a piercing, it will effectively cover it up entirely when necessary. Keep in mind that some companies simply won't hire you if you have a lip piercing, or they may prohibit you from getting a piercing once you've been hired.
Snip off the ends of the Band-Aid. You'll only use the adhesive part of the Band-Aid to cover up your lip stud. This way, the fibres of the cotton on the Band-Aid won't get caught in your piercing or ring.
Secure a square piece of the adhesive portion of the Band-Aid over the lip piercing.
Keep the other adhesive parts for later use, especially if you have to cover up your lip stud on a daily basis for work or school.
Replace the metal or glass lip ring with a clear ring. Clear lip rings can be expensive, but it's a good investment if you have to work in a setting where you're not allowed to have a noticeable lip ring. For example, professionals who work in health care settings are allowed to have piercings, but they have to be either filled in with clear rings or covered up.
Rub cover-up make-up on your lip stud. While make-up won't stick to glass jewellery, it will adhere to acrylic jewellery. Keep the make-up with you for the day, since it may rub off and you'll have to reapply it.
Invert the ring so that the ball part is inside your mouth and the stud is the only thing that shows on the outside. This will make it less noticeable, and if you choose to apply make-up, it'll make it easier to cover-up. However, this may be uncomfortable or impossible, depending on exactly where the lip ring is placed and how large the ball is on one side.
Always wash your hands before handling your jewellery or your piercing. Also, keep your lip ring clean by disinfecting it by swabbing it with rubbing alcohol. It's necessary to keep the jewellery in so that your piercing doesn't close. This is especially important after it's just been pierced. Ideally, you should keep a new lip ring piercing in for six months before changing the ring.