Last year, it was free to change dates without any penalty for economy ticket (L,M,K,H,B,Y class). This year. CX changed its policy and started charging $ 100 or $ 50 for date change.

I changed my date this year and paid $ 100 at aiport before CX staff could give me the BP. Luckily, I got my first upgrade due to overbooking on the flight from HKG to SFO after I showed the MCO/USD $100 to the check-in person. ( 1 op out of 16 flights--chance is very low)

The easy way to check whether there is a penalty or not is to check your E-Ticket. After you logged on you MPC account, you should be able to access your E-Ticket. On the Endorsement part, it will show the regulations for this ticket. For example, USD100REFND/USD100CHG and ext......