JIMCHI

Have award space in J & F PVG-HKG-SFO on KA/CX. When I booked this CX used "married segments" so that space was available PVG-HKG-SFO but not HKG-SFO. I saw that there were many PVG-HKG flights that were part of a "married segment" to the HKG-SFO flight. It wasn't until after I booked the space and was ticketed that I learned that PVG-HKG flights are notoriously late by hours. I would like to take an earlier PVG-HKG flight but F is no longer available HKG-SFO. I'm afraid that if I try to change the PVG-HKG flight that it will detect "unmarried segments" and cancel my F space from HKG-SFO. Has anyone ever tried to do this before and been successful without encountering major problems?