If I am self-employed, I send the government the entire 12.4%. Under the NRST, I keep the 12.4% and can give myself a 6.2% raise? (The 6.2% deducted from each paycheck would be returned, plus the company contribution of 6.2% is returned to the company to do with at it sees fit?)No, not unless you renegotiate with your boss (and I wouldn't be surprised if labor unions do this). The general consensus on the incidence (who really "pays" for it, not who sends in the check) of the employer portion of the payroll tax is that workers pay for it through lower wages. Remove the payroll tax and you would expect to see upward pressure on wages.
Now, how does this work if I am employed by a major corporation? Do I get the entire 12.4%?
If you are self-employed, then you would receive the benefit of the Self-Employment tax being eliminated asa well as your income tax. The only way that would not be the case is if your clients refused to keep paying you the same rate.