Set item field as editable in Sales Order regarding of header value

Go to tcode VOV7 and tick on the 'Business Item' in order to allow the item field to be editable.

For more information about how to create sales item category, please go to http://rukawaw-tb.blogspot.com/2010/08/creating-sales-item-category.html

Set Billing Block for item category

If you want to set billing block for certain material, it is best that you use item category to control it. Go to tcode: VOV7 and set the below setting in your item category.

Creating Sales Item Category

If you want to create new sales order item category, go to tcode: VOV7 and follow the below steps:

Create new item category as below:

Make necessary setting in the below screen:

If you want to know how to create sales item category, kindly refer to http://rukawaw-tb.blogspot.com/2010/08/creating-sales-item-category.html