PO Workflow after change quantity is changed down and unit price is the same

Hi,

if a revision of a PO is made by changing down the quantity or the price of a line, the workflow ends as soon as the buyer gives his approval action (so, no other persons who were committed in the previour revision are anymore called to answer notifications).

I would like to modify this behaviour, in order to have all orders changed to repeat the whole workflow.

Could you help me find a way to do this (I remember there was some standard option to operate with, but cannot find anymore).

thankyou