If you have a very common colour such as white...easiest thing to do is to buy another boot without the spoiler... Then you can swap back and forth depending what you prefer... rather than welding up holes and repainting.
yea, coulours a bit hard to come by, pantha mica with a green pearl so it would be a hole fill job, think about using car bog but theres just a hole nutin really for it to stick to if ya get what i mean? if i do use that and paint it with touch up paint will it have the same affect beasue it is a filler not metal?
to be legal make sure you put a third brake light somewhere on the rear window. maybe a monaro led one or intergrate the one off your spoiler into the top of the rear window or parcel shelf. a paint shop should be able to paint the boot for ya. wouldn't think that it would cost much. especially if it's off the car it makes it easier for them.
I'd still hunt around for that color bootlid...or buy / swap another spoilerless boot and paint that instead...even troll the car yards...maybe the yard might swap a bootlid to rice a car up in their yard in order to sell it....I wouldn't bother with a bog job...it will just crack and fall out...usually they'd reinforce it with some fibreglass underneath if they dont do it properly and mig weld it....but it will still weather and crack eventually...another holeless boot is the best way if you plan to keep the car.