Should I remove them? If so, how and when? Also my Xenia and mushrooms came on rock fragments, also what glue should I use to keep them on my rocks? My snails keep pushing them over.
You can leave the plugs and just let the coral grow naturally over them. I would use reef glue designed for reef tanks/coral. Its basically super glue and sold online or most fish stores.
You can cut the stem of the frag and glue the base on your rock. I use Gorilla glue (green bottle). To cut the frag, get something like that : https://a.co/d/0hnvnLdT
When you cut the frag, gently wrap the coral loosely into a clean towel so it doesn’t go flying in the room.