Payment term change on invoice with activities

Summary: business model requirement to have invoices created with installment plan, for example monthly, quarterly, semi-annual. Occasionally customer requests payment term change.

This change is easy if ar invoice has no activity associated to it. But once payment is applied or adjustment created the payment term cannot be updated

Content (required): current workaround is to issue credit memo for remaining balance on invoice followed by debit memo with updated payment term for remaining balance.

But this solution is cumbersome and doesn't connect well with business process owner.

Is there better approach to handle payment term change?

For example, customer invoice is for $1200 yearly contract with payment term for monthly installments of $100. After 3 months customer decided to switch to quarterly payment plan. Assuming 1st payment was due on January 1st what is best solution to update payment schedule in the middle of the March to have: