A W-4 is just a tool to get your employer to take the proper withholding. In my opinion, as long as AT LEAST the proper withholding is taken, you can fill out the W-4 any way you want. I think I would just do the line 4b method.
On the other hand, just leaving it as it is (NRA, and not changing anything else) would be fine too. It would just mean that your employer withholds more tax, which means when you file your tax return, you will likely receive a refund because you are allowed the Standard Deduction.
