It is possible to retrain traits in PFS, although it is cumbersome. My rogue/sorcerer arcane trickster wanted to pick up Arcane Knack (?) - the trait that allows you to regain 2 caster levels, which was not allowed originally, but was later added to the detriment of the existing players (Seems to be a lot of that in PFS). I took the extra traits feat, picked up Arcane knack and something else, then retrained the Extra Traits feat for 5 PA and kept the two traits I wanted.
I didn't actually plan to resurrect this thread, but I ran across it while searching for an answer to the question "Can you retrain feats which you are awarded when PFS rules take away the normal feats you would receive (Leadership, item creation)". I didn't find that question or a response.