Ability to update Accrue on Receipt Flag in PO Shipments

Our Client is in R12.2 and heavy user of Oracle Projects module. Majority of the PO are Expense based and currently Expense items are accrued on Period End. However due to business requirement changes Client would like to enable Accrual on 'Receipt' instead of Period end. We understand once the option is to accrue on receipt is enabled any new PO/ shipments will have Accrue on Receipt flag enabled but any Open POs (Unbilled Receipts) as of cut-off date will continue to have the old attributes and they will continue to accrue on period end. In order to make the