Add a purchase requisition line to an existing purchase order

Hi, 

I am using AX 2012 and would like to inquire whether it is possible to manually add an approved purchase requisition line to an existing purchase order. 

There is the option to manually convert a purchase requisition line to a new purchase order (from the "Release approved purchase requisitions" listpage) however I have not come across the functionality to add the purchase requisition line to an existing purchase order.

Has anyone ever managed the above scenario please?

Thanks in advance,

Alexia