You already have the answer for the federal superseded through ATX, but this topic came up earlier this season, and at that time when I checked, there were only three states (CA, UT, NY) that accept superseded individual returns. That means that if your client's state return(s) also requires correction and isn't one of those three states I listed, then you will have to create a separate file for the state amendment. It may be easier to process by amending both the federal and state at the same time.