Can the Revenue Accrual Method be changed once revenue has been generated?

R12.1.3 - Project Billing

Project was originally setup with the distribution rule of Cost/Event.  The revenue has been generating based on POC.  The project is now complete and we are trying to generate the remaining revenue.  When we run the Revenue Generation process it says there are no eligible events, etc.

In looking at the project Billing Information it shows the Revenue and Invoice methods as Event/Event.  In looking in the database, the Distribution Rule still shows Cost/Event.

Is there any way a user could change the Revenue Accrual Method once revenue has been generated.  Those fields appear greyed out on the Billing Information form.