Destination Organization field in Purchase Requisition

We are in 12.1.3. In Purchase requisitions, If the requester field is entered , then the Associated organization ( from HR Employee records) will be populated  in the  Destination Organization.  In our business case , in the same requisition - lines have to be created with multiple requesters associated with different Organizations.

During creation  of Requisition -consider a scenario  where  the creator forgets to change the requester on a specific line and saves the requisition. Now if he goes back to the line and changes the  Requester. But the destination Organization which has populated earlier - becomes a non editable field. So this cannot be changed  once you save the requisition or if go to Distribution  and get back to the line.