Hi, 

I think it is going to be difficult that the IRS will accept that change, Usually they do not allow to change from MFJ to MFS. They accept the MFS to MFJ but not the opposite. Even the worksheet in the form 1040 X says that. But good luck, I remember years ago, I have a case like yours and they accepted it, but I have to use a taxpayer advocate representative to help. Thank you.