Adding new line items to summary change record - REST Integration

Unifier - Version 24.9

We are trying to maintain the tree structured schedule of values, where same wbs codes are all siblings like the following image: 

We've tried replicating the way the API responds to GET requests with records with line items formatted how we expect, but see that fields like "uuu_sovlinum" will "not be updated during UpdateBPRecord call."

What is the correct way to add line items to a change order and have control over how the SOV will be structured via the REST API?