As I understand it, there was a policy change since I last attempted this.

Before, it worked just as you'd hope - no price change and both travelers protected on the original flight until they clear on the earlier flight. We made use of this several times, and if the earlier flight was wide open, we would even be confirmed and given boarding positions at the time of the request.

Since then, I don't think we've ever been formally told of a policy change, but others who have tried have been told that it doesn't work that way anymore unless both travelers have status. Agents have been asking for the price difference to make the change - I'm not clear on whether this actually yields a standby reservation where you are still both protected on the original flight or not. If the flight is still wide open (and there is enough time left) you might be able to remove your companion, be confirmed onto the earlier flight, and then re-add your companion to the new flight. I think you might have no choice but to pay the difference if the flight is booked heavily enough to prevent an immediate confirmed change.

​​​​​We have not had the opportunity to try this since resuming travel, and I don't expect to be in a position to try for quite some time. I'll be very interested to hear how it works for people this summer. Good luck!