Could I do the following on a 2-4-1 voucher
MAN-LHR-HKG outbound then add the return of SIN-LHR-MAN, i.e. different outbound and return destination/start?
If not, and I try the SIN route to SYD, can I book it in sections, i.e. LHR-SIN when availability opens up, then SIN-SYD when availability opens up?