Scott, What was the model number? You do need to be careful occasionally with certain models because it could be a flash board. For example small smoke with single element use a flash board that alters power to the single element smoke unit.
Otherwise in general terms a board swap is not an issue. Just load the sound file.
For a 3V to replace 5V just swap the 5V connectors onto the 3V board so the harness connectors fit. Change speaker to 4 ohm and change battery harness and battery to the 2.4V version vice 8.4V.
Could send me the boards, could be an audio amp failure, or something repairable. G