Purchase Orders and Receipts via EDI

We currently use the P4311Z1 and the P47070 to create PO's and Receipts via EDI. We are currently creating the PO and the Receipt once the PO has been received in our program. We would like to change this process so that we can create the PO once it is created in our program then send received and Un-received lines as they are updated in our program. We were told that we could not do this when we first set up the process but after working with this for over 2 years now we don't see any technical reason why