It can be changed before any flight segment (though often the agents do not do the change properly). It can be added retroactively if no plan was designated for a segment, but changing from one plan to another retroactively is difficult (not impossible, but very difficult). AS actually is a good idea. But QFF points can be redeemed for AS flights. I didn't know AS flies LAX-PSP (SEA-PSP is more likely). http://www.qantas.com.au/fflyer/dyn/...Points/flights

Just checked the AS route network, it is only SEA-PSP per http://www.alaskaair.com/as/alaska/i...qxroutemap.pdf