No, it's not possible to edit a pending order in Order Manager. The changes that you can make are:
- Add a Custom Product to an Order
- Add a Due Date to an Order
- Add a File to an Order
- Add a Note to an Order
- Add a Surcharge to an Order
- Add an Existing Product to an Order
- Archive an Order in Order Manager
- Change the Status of an Order
- Fulfill an Order with Order Manager
- Merge Orders with Order Manager