"Use APO scheduled order while combining in ECC" - this is done automatically when the APO Trim Order is sent to ERP and creates a Trim Order there. We never thought about offering a logic which converts an APO Trim Order to a ERP Combined Order.
The scenario without APO is the interesting one and the approaches I described above are referring to that.
To what you've written in response to Kai: The issue is really that an order which was created by an external system (e.g. APO - from ERP point of view) should not be rescheduled anymore. This is because ERP doesn't know about the scheduling logic which was applied earlier. For this reason even a standard Trim Order which was triggered from APO cannot be changed in ERP.
Regards,
Alfred