Hello KA,
Could you please let me know why you want to change the source of supply in ECC only?
Do you have PPDS? If yes then you can have one source of supply for that production version VB and transfer these orders to ECC system.
Apart from that if you want to do the development then check FM /SAPAPO/DM_PROD_ORDER_CHG_OLTP inside that with your own custom logic you can update the production version.
Best Regards,
R.Brahmankar