Everyone pretty muich knows you can take two Married Filing Separate Returns and combine them to one Married Filing Joint return. GENERALLY this has a better tax effect for the family.
But, can you take Married Filing Joint and split that return into two Married Filing Separate? The answer is YES… BUT it must be completed by April 15th of the following year….. i.e. 2012 can be amended but only up to April 15th, 2013. Extensions have no effect.