It's not that simple. The IRS has a 68 -page book for employers on how to calculate withholding.
Publication 15-T, Federal Income Tax Withholding Methods
Also, an employer can take up to 30 days to put a new W-4 into effect. So you'd better check with your employer and make sure you are going to be able to do what you want.
Why do you want to reduce your withholding for only one paycheck? What are you trying to accomplish? Maybe there's an easier way to do it.
