Some of these things might work, some might not work all the time. Priority baggage tagging will very likely work.
Extra baggage allowance is more tricky and it didn't work for me in at least one instance. Flying internationally on US I checked two bags for free, as per *G rules. When trying to change the FF number at the gate I was told that if I would do so, they would have to charge me for 2nd bag.
YMMV.