Be aware of the backing and make sure it's nothing you are allergic to. It's no problem as long as you don't take out the actual piercing. Make sure after you mess with it that you wash it and then apply with a cotton ball a warm mixture of water and sea-salt to help with healing (Sea salt soaks are the best!!). Professional piercing places could put in these awesome backings that are flat discs, I have them and they are better than traditional backings (called NeoMetal). If your piercing starts to pus, bleed, or smell go back to the piercer, there could be an infection. Good Luck!
I personally think that it's fine as long as the back is sterile and fits the earring well (keep the earring in the AT ALL TIMES). Oh, and always make sure that your hands are clean. :P
Yeah as long as you don't remove the earring that holds the piercing from closing
Try to to mess with it