Basically, I have 2 3ds now. One is my new personal one and the other is my old one and will be given to my sister. I moved my information over with my ID/system transfer then realized I didn't want to keep a lot of the friends I have added from off site trades (I wanted an entirely clean list and not of randoms from ACNL) however, there are some people I want to delete that I know would be upset if I deleted them. So I hard reset my 3ds while keeping them on my list knowing my list would be lost (therefore clearing my list and issuing me a new friend code). I believe they still have the old code added and will still think I have them added.

My questions now are:
1. Can they see any edits I make to my mii/name/games/status even if the ID is not associated with that code anymore?
2. Is there any way they can see my new code with this ID?
3. What happens to an inactive ID? (ie. not one tied to a system if I were to delink this one from my system?)