It depends on the value of the resistor and the data of the LED. Assuming it's an average LED with 20mA you would need a total resistance of 300 Ohm if you want to connect it to your 9V power source. So in case the already existing resistor is smaller than 300 Ohm you need to add another one until you reach at least 300 Ohm in total.
Does "light up switch" mean an illuminated switch? In this case you need to know the data of the LED or light bulb inside, most times it is the same as the working condition the switch is designed for. For example: in a switch that can handle 230v it is quite likely that the light inside needs 230V. If the switch is designed for 9V or slightly more, there shouldn't be a problem, but if it's lower you will need a resistor. (I would refer to the data sheet to be sure)
Or if you mean the switch to light up the LED from before you don't need anything else.