[otrs] Need Help with Customizing Subject Line in OTRS

Friends, My objective is to change the subject line of the ticket to the customer ID. Explanation: When a customer logs in and creates a ticket, the subject line of that ticket should be the customerID of the customer who is creating the ticket. Is there a way we could do this through the web interface or does it require editing the source code, if so which of the file(s) needs to be edited. Thank you in advance. -- Roopesh