After you file

No, unless you need to upgrade to a higher version to add something.  But you won't need to upgrade for a W2.

If it was Accepted,  you need to wait for your return to be fully processed and you get the first refund or your tax due payment has cleared.   Then you can mail in an amended return.  Do NOT change anything yet on your return until you start the amended return.   If you have changed it then take out the changes and put it back to the way it was when you originally filed.  You can fill out the amended return now but  it won't be ready to print it out  until mid-Feb

How to Amend
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed

You will get your original refund and get to keep it. When you go through the amendment section it asks you how much you paid or got back on the original return so be sure to enter it. Then the amended return will only show the difference you get back or need to pay. You can confirm this by printing your amendment and looking at the 1040X. Line 17 should be your original refund amount and line 20 should be your additional refund.  If you paid on your original return it will be on line 15.  If there is an amount owed with the amendment, it will be on line 19.

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