I have never changed the Customer Center Screen, now they are asking to do so. Where do I go to do it ? Scripted Record of Sales Order ?

Check out SuiteAnswer 51469 https://netsuite.custhelp.com/app/answers/detail/a_id/51469/kw/customer%20center%20login if you are asking for a custom login page. If you mean the dashboard after login then it is a published dashboard. Neither are scripted records or sales orders.