Before realizing that Form 1040X would not be available until March 25, 2021, I proceeded with making changes to a copy of the returns (Fed & CA) that I had filed and had been accepted. When the 1040X becomes available will I have to repeat the process of making the needed changes or will these changes be incorporated into the 1040X automatically? Will there be additional steps I have to take such as providing explanation of the amendments?
You must first UNDO all the changes that you made, and put the original return back to exactly what it was when you filed it. When you amend, the 1040-X asks about changes you wish to make, and prepares a completely separate form for those. And yes, you will have to explain the changes. Here are some examples:
o Forgot to claim a late arriving W-2.
o Added overlooked medical expenses.
o Corrected mistyped 1099-R.
o Deleted a dependent.