Correct, there are no changes fees on UA Shuttle fares ("SX" appears in the fare basis code). A fully unused ticket is full value; a partially used ticket can, however, be problematic, depending upon the agent.

Also correct, AA has no change fee on the routes it took over from QQ, including LAS-LAX, SJC-LAX. However, many (most) of their agents are not aware of this and you may need to ask them to double check the rules for the fare basis code on your ticket.