AR Invoice due date changing

Hi Team,

Some of our regular customers having some old outstanding (invoices falls in prior financial years) and which are already overdue as per the payment terms.  Now, as per the discussion, the customers are given some more time (from 6 months to 1 year) to settle their old outstanding.  They need to settle the current outstanding as per the normal credit day given (4 days) and every month they have to remit some additional amount towards the old outstanding.

The payment term we have fixed in the customer master is 4 days and which has already updated in all the invoices.  Now, as per the business requirement we need to change the AR invoice due date for the old outstanding bills as 180 days to 250 days.  At the same time, for the current business transactions the normal payment term 4 days to be continued.  Is there any way to change to AR invoice due date for the old outstanding bills?  Please suggest.