Track of Modifications In Blanket order

 Hello

 I am working  on JD 8.12  were requirement is  such that , they want to generate blanket order for the project  which will last till the end of project  ( minimum 2-3 years) . At regular intervals , the blanket Order Quantity  , cost etc can be revised and modified . So they want to keep track of all revisions done in the order and want to compare with actual blanket order at different point of time, so please suggest solution  so that Qty and cost at present can be compared with previous Qty and cost.

At present we are making Blanket order and then making Purchase and sales order from blanket. How can we achieve this in JD.