Skimmed through the wiki and I don't think my questions are covered.
1. Is SDC only applicable to AC-marketed fares (i.e. the fare owner is AC)? I have a LX-owned fare booked one of the segments in YVR-YYZ on AC.
2. For YVR-YYZ-ZRH-JNB, YVR-YYZ on AC, rest on LX, can I SDC for just the YVR-YYZ leg? Concierge told me no as SDC is offered for the entire bound YVR-YYZ-ZRH-JNB, and since there are non-AC metal involved, it's not eligible.
3. Does changing domestic part only for an international ticket invoke $100 charge (on business lowest) or $0? Ideally it should be $0 but realistically I think it would be $100.