You could make a spray paint drone like this one:
http://www.vice.com/read/katsu-shows...fiti-drone-456
Just fly it up to the light and unload some black paint over the light shroud.
It's a great solution if the light is on someone else's property and keeps you out of sight (you just need line of sight to the light for spoting and signal to the drone).
If you can get access to the pole there are extension poles that could be turned into spray paint can holders.
Shooting out lights is a bad idea and likely to get you in trouble - even in the NT!