Autopilot,
B-HLJ and HLK are msn 12 and 17 respectively being the first and second A330's built and were used for the A330 flight test program. Both were originally GE powered. After Airbus had finished their A330/340 flight testing they retained only msn 001, an A340 and put the rest of the development airframes into storage or up for sale.
CX bought the 2 flight test A330's which were refurbished by Airbus. HLK was re-engined with Trent's during the refurbishment. HLJ had already been converted to RR engines by Airbus for the Trent 700 certification effort. One of them (I forget which now) actually had both GE and PW engines on it while owned by Airbus so has been powered by all 3 engines.
Current COO John Slosar was head of Airline Planning at the time and negotiated the deal with Airbus.
With regard to swapping PW4056 and 4062 engines airlines (eg. United) that operate PW4062 powered 767's and 4056 powered 747-400 do indeed swap engines between the two fleets. The PW4056 is a derated 4062.