Changing the information in Box 12 with Code W on your W-2
on its own should not affect your tax return at all.
The information in Box 12 with Code W is pre-tax
contributions that were made to your Health Savings Account (HSA) through
payroll deductions. Since the money is
pre-tax, changing the amount should not affect the bottom line of your tax
return.
That being said, you may still need to file an amended
return because it will change the information reported on Form 8889 regarding
your Health Savings Account.
