R12--User Hook for Charges API

Hello,

We would like to explore the functionality of using custom hooks from charges....From the various documents here is what I understand

1) User Hook need to enabled

2) CS_Charge_Details_CUHK will have the specification and it is the responsibility of customers to create package body for CS_Charge_Details_CUHK

Can you please let me know if anybody has used the user hooks for charges to override any field Or populate any field in the charges based on the logic from user hooks...Iam looking for

a sample code if anybody has implemented this

Thanks,

Kiran