last minute equipment is so common on short haul routes - last time, HKG-SIN-HKG, my outbound flight changed from 33B to 77A, inbound flight changed from 772 to 74A, both within 12hrs prior departure.

Also, since there are 7(or 8) flights a day to SIN VS 3 flights to KUL, I reckon there are much higher chance for SIN flights with long-haul product, then you can change your flight.