Simply put the healthcare "fix" is a huge Constitutional no-no.
Why? Because when Congress sends the president a bill that they have Constitutionally passed and he signs it - it becomes law.
The president just can't add or scratch off something he wants.
The reason why the Supreme Court voted against the line item veto is that if any changes are made to a law after it has been enacted - it is no longer the law that was passed and it must go back through the same Constitutional process to become a new law.
The president just can't use a pencil. It must go back through the Congressional channel, again and get passed as an entirely new bill because that is what it is.
Now, when a president, after the law is enacted changes that law, he NULLIFIES the law. It is no longer the law that was legally enacted.
So, by Obama adding or sratching stuff off the law he NULLIFIED it.
Obama NULLIFIED Obamacare.
Did I mention the word - NULLIFIED?
Yes, and you are correct IIRC.