If you change your address, you should inform ICS. But if you move to another state in different service center, I think you still notify ICS, but I don't know whether you can still keep your case in VSC, they may transfer you case to CSC.
Redarding to AC-21, if your case was EB1, NIW, I don't think you need to fill AC-21.
If onther people have different answer, please feel free to tell us.
Thanks and good luck