How to Modify WF in Sales Agreement

Hi

I am working for a Client, where the Sales Agreements extensively used. If there is any chnage in Price for a Item in an Existing Sales Agreement then it should trigger Re Approval Process as per the Approval Hirarchy defined in Transaction Type.

If anybody worked / come across the above requirement, Please share your ideas how I can modify the WF in Sales Agreement.

Thanks in Advacnce.

regards,

Ramakrishna.