Redistribute the amount from header to all line items at invoice time

Dear members,

Hope you're doing well.

I am developing one copy control routine for below req.

<b>The problem is that fixed amount condition types that are applied to the header <u>manually</u> in an sale order are not updated at invoice time if the delivery has changed.[ If the order quantity or a substitution is made on the delivery, this value is currently being calculated incorrectly]</b>

In transaction VOFM, I have created new rountine and got condition rate (xKOMV-KBETR) from xKOMV(if condition was manually changed (xKOMV-KSTEU = C).

<b>My question is how can I redistribute this amount from header to all line items at invoice time? Is there any standard SAP function for this(to update invoice tables VBRK, VBRP).?</b>

Could any one please share your experience or knowledge about this?

Regards,

Srini