Well "amending" is not at all the process since that is not allowed. Even filing superseding MFS tax returns is a grey area. The bottom line is that when spouses sign a joint tax return they are "jointly and severally liable" for any taxes due, and as you can imagine it is an uphill battle to get the IRS to forget that.
File Superseding MFS tax returns, and if the taxpayers pay the full amount due you will be able to explain the situation to the IRS if any correspondence is received.
