Should Tax Classification Code be updatable on Purchase Order ?

Hello,

Trying to find out if a buyer can udate the Tax Classification Code on a Purchase Order autocreated from a purchase requisition.  I found Oracle notes that are contradictory:

Note 1495547.1 R12: Is it possible to override existing tax information or to add manual tax line in tax manager window for Purchasing module ? is stating that this is not possible:

     "No, for Purchase Order, we do not support Override or Manual Entry of Tax lines. That's why the option is disabled at Configuration Owner Tax options."

While Note 458218.1 Ability to Override Tax Calculated In E-Business Tax describes the steps to achieve it.