Changing Subscription Starts On date

Changing Subscription Starts On date

Is it possible to change the Starts On Date for a Subscription after the subscription and invoice have been created. 

For example:

The plan is for 15 visits in 30 days.

Customer signs up for a 15 visit plan on 1st of the month.
Customer pays the invoice on the 5th of the month
Customer visits the business on the 15th of the month
I want the Plan to expire 30 days from the 15th not the 1st.

One other complexity. The visit is recorded in Creator so an API is used to update the subscription.