Allow purchase documents to be converted to different accounting documents

Allow documents that have started in the purchasing module to be converted to different document types in the accounting module. We require any expenditure to be approved prior to purchase, whether it be credit cards, petty cash, student expense etc. I understanding in customer admin settings there is the ability to set the "accounting invoice document" and this is set as POIN, but if there is the option there surely it could also go to a ASCC for example (as per attached screen shot). But a default change wouldn't help as we wouldn't want all documents to going into the accounting module as ASCC, so the option to chose the "Accounting invoice document" type on posting and INV would be very helpful.