It all depends on the GAs.

CX does not have a publised op-up policy.

But based on standby priority, even you are a OW Emerald as AA EXP, your priority will be still lower than CX MPC DM.

But for sure, if J is overbooked, F op-up will happen if F can fit those people.

But Y>J and then J>F, not much chances.