Can I file a 1040X for the 2018's 1040 that I just filed last year in 2020?

[algoTTX]

Dear Tax Experts,

Last year in 2021, I filed a 1040 for my 2018 tax year, using itemized deduction.  I got a refund.   According to the 3 year rule(from the date of filing my tax return), I should be able to file a 1040X.  I know IRS have a 3 year limitation of getting a refund.  But my 1040X case is the other way around.  That is, I'd like to change my 2018 itemized deduction ($27k) back to the standard deduction ($24k) in the my new 2018 1040X, which will incurr a little less refund I could get, so that I'll pay a little portion of the refund from IRS back to IRS.

So my question would be:
1. Can I file a 1040X for my 2018 1040, since it's only 2nd year after I filed it last your (in 2021)?

2.1 If they would allow it, could my refund be nulled since it's passing three years?  This meant I have to return ALL the 2018 refund that IRS sent me?

2.2 If IRS would allow my 1040X, and if IRS won't null ALL my 2018 refund, do I just pay a little portion of the overpaid refund due to my 1040X will change the original itemized deduction (27k as I used) to the standard $24k deduction?

Thank you much for the urgent help, since the 2021 is in the corner! 

Bless!

al

[Mike9241]

the 3 year limit is if you are due a refund. there is no limit if you owe. not only would you have to pay back a portion of the refund you got but also late payment penalties and interest.   

[DavidD66]

In order to receive a refund, generally, you must file an amended return within three years from the date you filed your original return or within two years from the date you paid any tax due, whichever is later. If you filed your original return before the due date (usually April 15), it's considered filed on the due date.  There is no deadline if you making a payment.  

If your amended return results in you owing tax, you will need to make a payment when you file your amended return.