You could do this through an "Action Rule" by modifying the ticket. So, if you have this custom field for all Request Types, you could just set it at ticket creation to modify the ticket and select '2' for your custom field for all new tickets. If it is only for a certain request type, you can narrow that down as well. If the '2' didn't apply for the ticket, your techs could just make the change when working the ticket.
Have fun!