What is the impact if we use the UserDefined Fiscal Classification in AR for reporting purpose only?

There is a requirement to reflect the withholding tax (WHT) amount in the face of invoice. Since we cannot use the customer set up to derive the WHT per invoice because there are instances that invoice with multiple lines has different WHT rate. With this, we try to use the User-Defined Fiscal Classification to properly identify the tax rate per line then create a formula in the invoice printing. Is there any impact if we use this approach?