I had a Z class the other day for KUL-SIN... the person at the ticketing counter checked and said it’s a business promo fare and would cost me a rather hefty change fee to move to an earlier flight. Tried again at the lounge and got the same response. I refused.

Which is silly because the earlier flight was rather empty in business class. Plus because now I had to spend longer time at the lounge, it was actually more expensive to MH due to the many more glasses of champagne I had drunk!