Update Shipment Set During the sales order revision

Summary:

Requirement : There are 2 lines on the sales order. Shipment Set - 1 is assigned to both the lines. Later on customer need to assign different shipment set to line number 2.

When we tried to revise a sales order and edit the line number 2 with the different shipment set and we are unable to do it.

"Create" Option is greyed out.

Thanks,

Sandhya