WHMCS Action Hook

We need an Action Hook that allocates all the relevant Invoices on a client account to Debit Order once this option was chosen, regardless of the payment methods chosen thereafter. In other words, even if the client changes the payment method on a new product in the client area under the same account - all the current outstanding amounts are added to the Debit Order Report of WHMCS automatically. Thereafter only admin should be able to make changes.