You're correct JD, that's for the type bmbahia is flying, A-320/30
You're also correct regarding the second point.
But as usually QNH is updated as soon as it changes, the variation is so little, therefore we almost won't notice anything on the altimeter reading after the update.
If a sudden change in the altimeter setting was possible, 29.92 to 29.42 the pilot would have to initiate a 500 feet climb to go back to 5000 feet altitude.