@efeliciano , while agreeing with the expert @SwapnaM , I am uncertain as to what you are trying to do.
First either you are married or you are not. If married , and you spouse agrees , then you generally file MFJ ( Married Filing Joint ) and getting generally the best tax outcome.
If you are considered unmarried ( for tax purposes ), and have qualifying dependent(s) then Head of Household ( HoH ) is the next best taxwise.
So I don't understand the facts and circumstances that would legally allow you to switch between MFJ and HoH. You could between MFS and HoH ( but why would you ).
pk
