[Remove incorrect information}
See this TurboTax support FAQ for amending a 2017 tax return originally completed and filed using TurboTax - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-a-return-in-turbotax/01/27372
I beg to differ ... you CAN amend to change to either MFS OR MFJ ... however what you cannot get are credits listed below ... just remember that the spouse's total worldwide income must be entered on a joint return so choose carefully ...
The Protecting Americans from Tax Hikes or PATH Act made several changes to the tax law, including preventing retroactive claims of the EITC and CTC by amending a return or filing an original return for any earlier year in which the individual or anyone listed on the return did not have a SSN valid for employment. You can't claim EITC or CTC unless the Social Security number for you, your spouse (if married filing a joint return) or a qualifying child is issued before the due date of the return including any valid extensions.
http://www.thetaxadviser.com/newsletters/2016/jan/congress-makes-changes-to-popular-tax-credits.html