How to update Timesheet line Item through interface like DI API or other way?

Hi,

We are adding support for Timesheet object where we need to provide support for update timesheet programtically and using external system. We use DI API for this in .net. When we use UpdateTimesheet API, it generally delete all line items and add the line items that we sent. So What is the exact way to update time sheet? Is this the intended behavior?

Our use case is to update specific line item. So for this should we query entire timesheet object and then modify appropriate line item and send again entire timesheet object?

Is there any other API to modify just line item?