Add new schedule lines with BAPI_SALESORDER_CHANGE

Hello community,

I am about to use the BAPI function called "BAPI_SALESORDER_CHANGE" to insert new schedule lines to an existing Sales Order with let's say 1 Item and 2 existing schedule lines. I suppose I have to set the "UPDATEFLAG" for each new schedule line to "I" for insert. Furthermore I need to refer to the Order Number by providing "SALESDOCUMENT" and so on.

Do I need to provide the parameter "SCHED_LINE" to the BAPI call in order to add a new schedule line?

If so, what value would I use for "SCHED_LINE" ?

If so, can I use any value not already used by existing "SCHED_LINE" fields for that specific item?

If not, what happens with that Sales Order when I do not set "SCHED_LINE" ?

Thanks in advance!