You can do one of two, or both things to adjust the headlights. Either try your best to twist and jiggle the bulb in the housing to get the best optics, or you can use the stock adjuster tabs on the stock housing
You misunderstood. A retro fit is when you take the entire HID system from a car that came with HID, and you put it into the headlight housing of a car that didn’t have it from the factory. Like on my Nissan 300ZX for example. I put Acura TSX projectors in, and bulbs, ballasts and ignitors from a Subaru STI. On my Datsun 200SX, I put in projectors, bulbs, ballasts and ignitors on from a Mercedes E55 AMG. That setup is BiXenon, where it has the movable shield to switch from Low Beam to high beam on just one bulb.
If I remember correctly, the Lancer did not have a stock HID system.
How they make it look good, it really depends. But an efficient HID system is not about how “sexy” it looks from a spectators view, but about how good the optics are down the road and how well it minimizes glare. One good thing that people can do to minimize clear, is with standard Projectors, when you spray all chrome pieces to flat black, that reduces the amount of apparent glare from the housing. The colour means jack shit. In fact, if it’s blue, the amount of outward light is crappy. The ideal is WHITE. Usually WHITE only displayed at the 4100 - 4300K mark. Getting up to 6000K is way too blue.
I have no idea what you mean about the bulb cap, but I was saying that based on the type of system it is, they had no choice to remove the highbeam.