Hi,
If you make changes in the pricing procedure, you can post the deductible tax amount in GR using some other condition type. But this will affect your tax reporting, which is a legal requirement and hence its not suggestible. .
If the complete liability amount is only for reporting purpose, I would suggest to modify the reports to show the full amount in additional custom fields, without touching the best practice. You may use the FM: CALCULATE_TAX_ITEM to calculate the tax amount based on PO number and GR quantity and display the same in the required reports.
Regards,
AKPT