Suggestions:
For shifting a balance of a customer invoice wise to different customer code following process to be followed:
1. Misc Credit note with balance amount of invoice for each invoice to be passed in the customer code from where balance needs to be removed.
2. For each outstanding invoice in the customer code from which balance needs to be shifted , A Misc debit note to be created in new customer code in which balance of old customer needs to be shifted.
3. A receivable JV to be passed to adjust all the credit notes created in step 1 against all outstanding invoices. Net amount of this JV should be 0 .
These steps need to be done to knock off all invoices against the credit note of the customer from which balance needs to be removed(old customer) .