How can we default the Order type on the Sales order form with users being able to override it later

Summary:

Requirement:

Business has multiple entities across geographies which share a common list of Order types in the Order Management module in Oracle Fusion. Since majority of the orders created by them will be Standard Orders, the requirement is to default the Order type on the Sales Order form as 'Standard Order' whenever they open the form to create a Sales Order from UI.

Issue:

To achieve this, we defined a Pre Transformation rule which defaults this value on Order type when Business Unit is not blank. With this rule published, when we create the Sales Order, the Order type is defaulted, but the system is not allowing the users to update the Order type to some other value and submit the Order.