On the earlier switches (which I think might apply to the 4A, not sure), you insert the key and turn the switch to the ON position. Then there is a hole in the body that lets you depress a pin, and pull the barrel out with the key.
But a TR6 would probably be more like my Stags, where there is a roll pin through the switch body that retains the barrel. Tap the pin out with a punch & hammer, then again pull the barrel out with the key.
Not sure what tabs you are talking about, sounds like the ones that hold the switch itself together (which is a separate assembly from the lock on later cars).