So as far as "A" is concerned, do not declare the second ball provisional - just play it as your third stroke. There is no requirement to declare it provisional so if you wish to abandon the first ball, do not declare the new ball provisional. Also, if your opponent finds the first ball you are not required to play it as it lies; you always have the option of declaring a ball "unplayable" and you can take the appropriate relief of "two club lengths no closer", "keep the spot where the ball is found between you and the hole" or "replay from the original spot".