Closer reading of the rules does seem to indicate that the extended due date is not recognized for changing irrevocable elections, so it seems like there is no way anymore for me to properly file a superceding return to change the original return information. Best chance at this point is filing a regular amended return, but IRS's current ridiculous processing delays (>9 months) make it seem pretty impossible that I could provide official verification of the amended return changes to the original return by year end. One good sign is they now seem to be promising that forgiveness applications will be processed thru Dec. 31, 2023, which would give enough time for IRS to get these handled.
IRS accepted my e-filed amended return to change filing status from two separate MFS returns into one MFJ return, so at least in that scenario (where both spouse already filed), e-filing to change filing status seems to work now (so far).
I think it is very likely that DOE will utilize the IRS Data Retrieval Tool (DRT) to verify the student loan forgiveness applications, as they already use that for processing their Income-Driven Repayment (IDR) program applications. That tool, however, doesn't normally report any amended return changes to DOE. Have to hope they will also have a provision for manual review in cases like an amended return (and more particularly, pending amended returns that change the filing status and thus change the income limit for program eligibility).
