I would like to change the tickets history that is showing when you start to create a new ticket based on the customer user that is starting the ticket creation and not on the Customer ID as is the default. Any guidance? Thank you.
Do you mean the open tickets that show on the right-hand side, in the Customer Information box? You can add history for the customer login rather than the customer ID by enabling
Frontend::CustomerUser::Item###16-OpenTicketsForCustomerUserLogin and disabling Frontend::CustomerUser::Item###15-OpenTickets in SysConfig.
If you'd mean the list of tickets that is shown on the bottom of the screen, the limitation to searching by customerid is unfortunately hard-coded in AgentCustomerSearch.pm so changing that would need code changes.