Ah. Perhaps. Would you be looking to change BOTH portions of the trip (outbound and return) ? If not, you have to worry about whether the remaining L fare one way is combinable with whatever you change to the other way.

If you change the roundtrip, I believe you may have to pay a change fee in addition to the difference in fare.

And if I remains at 0, you still are likely not to clear before the gate.

Simon