it should be possible by using the exit M06E0002
you only need one characteristic CEKKO-USRC1, which is for example either Y or N.
if it is Y then the strategy gets triggered, if it is N then the strategy is not triggered.
In your coding in the user exit you check if it is an order change or order creation e.g. by checking sy-tcode . in case it is a change you move Y to USERC1, otherwise you move N.
Purchasing: Release Procedure for Requisitions and Other Pur