Welcome To FlyerTalk.

Just call in and state you have already book and paid (non-refund) a local tour at SFO for your initial 12 hours layover, hence this will not work. But do first research what route are available before you call, so you can present that option to the phone agent right now.

Also the YVR-HKG flight will be on the new 777HD, so if you are one of the people that do not like the new config, this can be another reason for your complain as well.