Yes. When smaller jewelry is put into a piercing that was pierced at a larger gauge, the piercing will shrink slightly to accommodate it.
However, you must be careful when shrinking piercings. If you put in a smaller stud or piece of jewelry then the hole size, it can sink inside of it. Lips are notorious for having small studs sink inside. Ask a piercer for advice when downsizing piercings to be sure that sinking doesnt happen. Sometimes just putting a bigger ball on the end of the stud will keep a smaller post in a piercing, so it doesnt sink.
A dot piercing is a piercing that has a stud.
Usually a week ( 7 days ) or longer (14 days), it is important that the swelling has settled, if not wait a bit longer. If the stud is too short it can damage the piercing if for some reason the piercing swells up again.
you should use a stud
Gee I wish people would learn the terminology before they ask questions, we don't pierce anything with "studs" they are called "barbells", they can be bent or straight curved or circular. The phrase "stud" is a rude phrase to describe an ear piercing "stud" which is never used in professional body piercing. Now as for your lip, yes it can be pierced with an 18g barbell be it straight or curved.
When you first get your piercing, with any piercing, the people that do the piercing they use their own equipment and normally you choose they kind of stud you want. So yes you do have to get a stud first. Normally you have to wait 6 weeks before you can change any piercing, just so your skin can get used to it and also to decrease the risk of an infection.
The jewellery for piercings isn't something you buy off the shelf, the piercing needs to be measured and size according to what you were pierced with and where the piercing is at with the healing. You need to see a professional body piercer to get the appropriate jewellery for your piercing.
If it's a vertical Labret piercing then it's a curved barbell, if it's a standard lip piercing it can be a labret stud or a ring.
A clear piercing retainer
pull the stud out
Your piercer can, but you should not attempt it as you could injure your new piercing and it could lead to infection.
It's best after the piercing is healed, otherwise it might get infected and swell up.
its called a stud.