How can we improve WHMCS?

I am new to WHMCS so I am not sure of the issues. But it is common to have to modify and existing invoice. The example is invoice has been issued but the client want to change say the billing cycle. There should be an option to do this where on click the existing invoice is cancelled and or deleted, the billing cycle and any applicable items changed and whmcs then re-issue the invoice.

Currently the process is cumbersome - and made worst if the item is part of a multi-item invoice - you have to split it and here whmcs does not retains the billing dates it changes the new invoice to today date and due date 14 days out in the future. This makes no sense.

But regardless, now that the item is in its own invoice it can be cancelled and deleted. Then you can make the changes and must set the next billing date back 1 day then re-issue the invoice and once paid only then you can fix the billing day back to the proper.

More so if you update the product billing cycle and then edit the invoice updating the cycle and pricing info and the fee -- then in the db set the next invoice date - this works. Hence the tool is possible and eliminate the work around or direct modification of the db which is not recommended.