Cannot Change Liability Charge Code on PO

All,

I will appreciate your input on this issue, the user created a requisition which was for an Inter-company Account using the wrong Charge Account. We need to reverse this problem, we are able to change the Expense Charge Account but not the Liability Account.

User attempted to create another PO using the same Requisition the Liability Account was still the same because the code defaulted from the Requisition. Here again we are able to change Expense Account but not the Liability Account. 

Based on the above I have the following questions: 1.  Can a Liability Charge Code Account be changed on a Requisition after it’s been saved and converted to a PO?