I changed mine a couple of months ago and to confirm you don't need to take out the spoiler to replace the high level brake light (it's a standalone part). I applied masking tape around the old brake light to avoid scratching the spoiler and then proceeded to use a pry tool and screwdriver to pierce through the plastic lens (it does feel a bit daunting stabbing your own car!).
Once the lens are broken you can pry out the plastic base and disconnect the wire. From there you can just swap over to the new part and place it back in (though you may want to test that it works fine first before snapping back in the spoiler!).
Think you can only get this part from the dealer/TPS, don't think there is an aftermarket version for these on top of my head.
