I'm assuming that you either have a lot of OT or that you are going to be paid a bonus soon.
If you're wanting to change your W4 because you'll be receiving a bonus, your employer may treats is as a "lump sum":, then they will withhold 25% no matter what your W4 says. ( I work for a company that pays us a 'bonus" and they always treat it a a lump sum and withhold the 25%)
You can change your W4 (although the above expert is correct, you should not claim "exempt", you should increase the number of allowances you claim. For example, if you are claiming "Single/0", you may, want to change it to "Singe/15" with your employer's permission (some employers only allow you to change your W4 at certain times of the year, or they have a limit of 1 change per year, meaning you would not be able to change your W4 back)
The other reason you need your employer's permission is that the IRS may review your withholdings (I understand that you don't plan on making the change permanent, only for 1 week), but the IRS also audits employers so that they don't allow people to claim "exempt" when they don't qualify, and to make sure that the employer is following the IRS guidelines.
Please see below:
So, the answer to your question is....can you claim "exempt"? No
Can you increase the number of your exemptions/allowances on your W4? (I think the top number you can claim is around 15, so in effect, over claiming your exemption/allowances will accomplish the same result as claiming "exempt" Again, this is at the discretion of your employer.
Can you increase the number of your exemptions on your W4 for 1 week and then change it back? Maybe.
First, you have to find out if your employer will allow you to change your W4 for one week.
Also, you will need to find out how long it takes your company to make the change in your payroll. According to the IRS pub I referenced above, it can take up to 30 days.
As you can see, this isn't just a yes/no answer, and the reason is the new guidelines the IRS instituted making employers carry some responsibility for not allowing their employees to claim exempt when they're not, or to knowingly allow a employee to vastly under withhold.
I hope this helps.