You need to change standard sales processing logic and your requirement cannot be met in Customizing.
What options will ensure there are no changes to SAP-delivered objects? Note: There are 3 correct Answers to this question.

Where do you control the billing relevance? Please choose the correct answer.

Where do you configure the default billing type to be used for order-related or delivery-related billing?

You investigate the standard behavior of the two sales document types Delivery Free of Charge (FD) and Subsequent Delivery Free of Charge (SD). What do you find out? Note: There are 2 correct Answers to this question.

Which time components are used to calculate the confirmed delivery date in a sales order? Note: There are 2 correct Answers to this question.