How to default Accounting Rule and Invoicing Rule on SO line from item level through OM Extension?

Hi Team,

We have a requirement to default Accounting Rule and Invoicing Rule on Sales Order lines from item level. Previously we defined Pre-Transformation rule for this requirement. But the Pre-Transformation rule is not getting invoked for orders created through REST API. So we decided to go with the OM Extension.

When we started to define the OM Extension we found out that the ItemPVO has only AccountingRuleId and InvoicingRuleId attributes. Where as at order line we have AccountingRule, AccountingRuleCode, InvoicingRule, InvoicingRuleCode attributes. AccountingRuleId is different from AccountingRuleCode and the same goes for InvoicingRuleId too.

So please help us in defining an OM Extension to default Accounting Rule and Invoicing Rule on Sales Order lines from item level.