Third Brake Light - Should be able to squeeze the side and pull it off or use a screwdriver to pop the casing off...then there should be some bolts you can remove to get the the bulb.
DeYellowing - Seen it done, heard it done...can't remember how, but i'm sure you can do a search on here for it. Or go the easier route and just buy some red and clear tailights.
Ractive Intake - Not sure about it, i have an Arospeed intake and you can't tell the difference at all. I don't believe you would be able to actually feel the difference with the Ractive, but i really can't say from experience. Even with a Weapon-R i can't feel any difference. But ya know.
Good Luck