Could I replace new ear piercings with something else or..?

You have to keep the starter studs in for 6 weeks. Taking them out so soon will be very painful as the skin is still raw and hasn't healed. Believe me, it hurts even after 5 weeks I took mine out and it was painful. You also risk infection taking them out too early. No retainers either.

I was told to keep my new ear piercings in for 3-6 weeks before changing them so that you could allow them to heal properly.

I personally heal quickly, so i only need about a week and a half - 2 weeks before i can change my ear piercings without worrying, but i don't recommend doing so unless you are completely sure they are healed. Indicators would be that the don't sting or hurt when you touch them and when you clean them you don't get as much discharge or crusties off of them. and if you change them early i would continue to clean them because as always with a bit of metal shoved through your skin you can get an infection.

so, if you think you are healed and are willing to take the risk from switching earrings before the prescribed date then you can, but it's really not suggested.

hope this helped!