Correct use tax on paid voucher

Hello,

In PeopleSoft 9.2, while reconciling use tax, it was discovered that a voucher was marked for use tax but should have been tax exempt. This can be corrected by a GL journal entry, however correcting the error in the AP submodule would be preferable. It looks like this cannot be corrected by entering an AP journal voucher, backing out the original line with use tax and entering a new line as tax exempt, because the AP journal voucher default is tax exempt and it is uneditable. I'd appreciate suggestions for making this type of correction.

Thank you