Hi,
Can you give more business background why you want to change material number in the document number in BSEG?
Once you do goods movement with a movement type, system creates material document with accounting document based on your setting in material type (OMS2) of your material. In your created accounting document for material, have the respective G/L accounting entries( Stock account, G/R clearing account on goods receipt) and if in case, material is not stock material with quantity and value updates, then your consumption account triggers against G/R clearing account on goods receipt for purchase order.
If you and your business do not need that accounting document for material which is posted in your system, then cancel that document and correct transaction data in purchasing with your favorable material number and post document in inventory management with transaction(material document with accounting document) with your favorable material number.
Regards,
Biju K