In addition to being able to configure how packages are billed when they are added or suspended, you can now also set a separate rule on how subscribers will be billed after their billing settings are changed.
This setting can be accessed through the Settings window -> Billing -> Invoicing -> Prorate Options panel.
See our help file for Prorate Options for more details.
For an example of how changing the billing setting would look like, see screenshots below:
Invoice before the billing setting change (annual billing cycle):
Billing cycle changed from Annually to Quarterly, with the indicated option selected in the prompt:
Invoice (annual) after the billing cycle change — annual item has been reversed: