HI,
In the Application and User Management you can define an approval process for sales orders with the following possibilities:
A multi step approval considering several approving parties,You can define conditions for certain values such as
1. profit margin
2. total discounts
3. total
4. net value
5. ABC classification
6. project-based
7. credit status
. so for your case you can set the approval process for total or net value so there is any change for line item it go for approval.
hope this helps you.
Regards,
Suresh