We want the list price to be updated based on different attributes

Summary: While using Subscription Management, we want to bill evergreen subscriptions i.e. the bill lines are going to be generated for each month, we have two attributes CPI Adder and Base Price through which we are calculating the list price. We have used 'Get Base List Price for Goods and Services' to update the list price the first time, but once the subscription is active and invoice generated for the first line , it is not updating the list price when the attributes value are changed. Please let us know if we can achieve the requirement.

ListPrice = BasePrice + BasePrice *CPIAdder/100;