How can we improve WHMCS?

We want our customers to be able to change their default payment AND the payment on a per product basis like what available using this marketplace add-on https://marketplace.whmcs.com/product/4998-set-default-payment-method-per-product …. Scenario: a single customer may have 5 different products and 5 different payment methods. The customer should be able to login to the portal to change the payment method on a per product basis. Right now they can only change their default payment method that would affect future orders. If they want to change the product default pay method it can only be done on the admin.