Default Setting for BSEG-REBZG field in all Sales Orders

We are looking at setting a default value for the BSEG-REBZG field so that the due date for the Sales Order is determined by the payment terms?

How do we stop these from being due immediately after creation?

We have the same issue and here's what we did to resolve it:
- create a user exit to automatically populate the "Invoice Reference Field" (BSEG-REBZG) for all credit memos.

Also, refer to OSS note 17410

     SAP Note No. 17410                           19.03.2003
     ________________________________________________________________________

     Number              17410
     Version             6 from 17.12.1998
     Set on              17.12.1998

     Language            EN
     Short text          Posting credit memos; payments and dunning

     Responsible         SAP AG
     Component           FI
                         Financial Accounting
     ________________________________________________________________________

     Long text

     Symptom
     Payment terms for credit memos not functioning as expected:

     1.  When credit memos are posted, the payment terms are not taken from
         the customer or vendor master record as is the case with invoices.

     2.  During dunning or payment runs, the system does not take the payment
         terms entered in the credit memo into account.

     Additional key words
     F110, payment programm, SAPF110V, SAPF110S, F150, dunning program,
     SAPF150V, due date
     Cause and prerequisites
     Works as designed.

     1.  Credit memos are either referenced to an invoice or not. A credit
         memo with an invoice reference (field BSEG-REBZG) has exactly the
         same payment terms as the invoice.

     2.  A credit memo without an invoice reference is always due on the
         baseline date (the exceptions to this are credit memos which have an
         explicitly-stated value date).
         Credit memos of this type have the indicator "V" in addition to the
         specified payment method in field BSEG-RFBZG (see online
         documentation for this field).

     Solution
     Credit memos that have a reference to an invoice should be posted using
     this reference (when processing in the background, you must fill field
     BSEG-REBZG accordingly).
     Credit memos that refer to an inoice or have had other terms explicitly
     specified for them should be posted as credit memos with a fixed value
     date (with batch input processing, put a "V" next to the payment term in
     field BSEG-REBZG).
     Source code corrections
     ________________________________________________________________________

     Note is release independent

     Further components

     FI-AP
      Accounts Payable
     FI-AR
      Accounts Receivable
     ________________________________________________________________________

     Reference to related Notes

     Number    Short text
     ____________________________________________________________
     166672    MR1G: Credit memo with Invoice Reference
      84137    Line items: payment date for credit memos
      79871    Due date for net payment with credit memos
     309199    Pstng credt memo - dys in arrears w/ clearng incrct
    _____________________________________________________________
 
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