....The most obvious/dangerous (and unfortunately cheapest/easiest) change people make is retrofitting an HID kit into a halogen headlight assembly. This more than TRIPLES the amount of light output, which a halogen assembly can't handle safely (too much light in the wrong places). The assembly was designed to aim light from a specific halogen bulb with a regulated filament position (even differing halogen bulb types have filaments in different positions and different spiral axis, so each and every headlight assembly is designed to match a specific bulb). Because you're dealing with extremely short distances between the filament and reflectors, tiny variations have huge affects on light direction. This is why it is recommended to re-aim your headlights after a bulb change.
Changing the luminary (in this case halogen to arc discharge) compounds the issue; HID is a high-output gaseous arc that illuminates from a different physical position and in a totally different manner than a halogen burner. The light hits the reflectors from unusual angles, which results in a massive amount of glare that can blind other drivers. Studies have shown that glare causes drivers to lose spatial awareness and unintentionally steer toward the bright light (i.e. you). I'll leave it at that, but this mod is very dangerous for many many reasons and is NEVER legal. Please don't do this, for your safety and the safety of your fellow drivers.
So you have a couple of legal options. As njjoe mentioned, you can swap out your halogen projector headlamp assemblies for legal Murano HID projector assemblies; 3x the lumens and safely-aimed, but expensive and not plug-and-play.
2009+ Muranos lucked out because they can easily swap their H11 bulbs for H9 and more than double their light output. These two bulb types are physically identical; the only difference is wattage.
H11: 55 watts, 1,000 lumens nominal
H9: 65 watts, 2,100 lumens nominal