The scoops are interchangeable, the splitter is the metal part on the underside of the hood. You should swap both out when usually going to a bigger TMIC, but other than that reason Im pretty sure theres no benefit to swapping it.
The spoiler is only bolted onto the trunk. You have to take it off from the inside of the trunk (8bolts/screws I believe). And the light should just unplug from the harness. If you remove the spoiler you will have holes in your trunk for water and what not to get in, so be mindful of that.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX