RE: Changing Switch
This is the standard Futaba trainer switch:
FUTM3680 ML-1FLP SWITCH TRAINER LONG $5.79
It can be ordered through any Futaba hobby retailer. The switch must be soldered to a circuit board and then screwed to the transmitter case with the dress nut.
If your switch is not the standard part, it may not fit onto the circuilt board properly.