YMMV but IME, you'll have little to no luck getting a SDFC to a different routing when requesting on the phone with an agent. The rules are strictly followed. You could HUCA and I bet after a dozen times, you may get an agent especially at the EXP desk willing to accommodate you.

Now when you go to the airport on day of flight, you could have much better luck. When there are disrupts and IRROPS at that particular airport or another airport or even systemwide, the airport agents are more likely to get you to your destination sooner and quicker than on the routing you originally booked. Ive been successful several times when theres delays with both weather impacting the East coast as well as mechanical delays. One situation Ill never forget was routing from LAX to JFK via CLT due to it being hundreds of dollars cheaper than the non-stops. I was able to SDC to a nonstop LAX-JFK and I then managed to clear a complimentary upgrade into J lie flat. This situation occurred while there was a hurricane hitting Florida. Request was fulfilled via a Flagship lounge agent at LAX.

Even when there are no disrupts etc, you may still find a helpful agent that just wants to get you on your way and will work the system to your advantage. Just know that the rules state otherwise and to just be very nice and not demanding when requesting a change. You'd be surprised that the way you request something from someone can have a massive impact on the outcome.