@Jennifer_McCarroll There is no tax rule preventing you from switching from MFS to MFJ or MFJ to MFS from one tax year to the next tax year.
For example you can file as MFS in 2016. In 2017 file as MFJ. In 2018 file as MFS, etc.
What you may have seen is you cannot switch from MFJ to MFS after the due date of the tax return for the current tax year.
But you can change from MFS to MFJ in the current tax year. So amending your 2017 tax return from MFS to MFJ is allowed.
