If I book a United codeshare on US Air metal can I do a same day change within the 24-hour window to a United flight?

Specifically, I am looking to fly HNL - LAX and on the date I need to fly the United direct flight is significantly more expensive than HNL-PHX-LAX on US which I can book through the United website. I would like to do a same day change to the direct flight if possible within the window. I have had good luck doing this in the past booking HNL-SFO-LAX on UA when there was a similar price discrepancy and SDC to HNL-LAX 2 to 3 hours prior to departure (and even scored a CPU!). Will this work on a US codeshare though? Would SDC still be free as a 1P?

If not I'll just fly the HNL-PHX-LAX route, but it would be nice to take the direct flight.

Thanks!

-Erik