You can edit either one line item at a time or multiple line items at once.
Edit one line item at a time
To edit a line item's pricing, delivery, and other settings:
In your DoubleClick for Publishers account, click the Orders tab.
Click the order containing the line item you want to edit.
Find the line item you want to edit. You can search for the line item or view the line items in the list.
Click on the name of the line item you want to change, then make your changes on the Creatives and Settings tabs.
Edit multiple line items at once
You can bulk edit flight dates, rates, and goals. If you're bulk editing rates and goals, all of the line items you're editing must have the same rate type (CPM, CPC, or CPD) and goal type (impressions, clicks, or weight).
To edit multiple line items at once:
On the "Orders" tab, click the order containing the line item you want to edit.
Either select the check boxes of the individual line items you want to edit or click the check box at the top of the check box list to select all line items.
The "Bulk edit" screen displays.
Make your changes and click Save.
Can I change a line item's advertiser once the line item starts delivering?
No, you can't. You'll need to create a new line item under the right advertiser.
Yes, you can. Reporting on revenue metrics will be based on the rate when the ad served.
The start date can't be changed if the line item has already changed to "Ready" or the line item has begun delivering. However, if line item still needs creatives and hasn't been manually activated, you can change the start date.