I do not think that they will charge you the $10 for changing the routing over the phone.
The ticket can be changed on-line however, so, they may want to charge you the $10. If you are choosing a routing that can't be booked on DL.com or you get an error message, then they definately shouldn't charge you. Worst comes to worst - tell them dl.com comes up with an error message. The tech people at the dl.com desk will change it for you.
SR