I changed low headlight from halogen 9006HB4 to LED 120 watt.

Then i knew it may cause problems.
so does this may cause problems?

And can i change high headlight with 800watt or how to calculate this?
and the reverse light want to change it from 5 watt halogen to 16 watt led. Is it possible?

 

Why do you need 120- watt and 400 watt led bulbs? Honestly that is dumb. 35 or 55 watt led bulbs for headlights is all you need and any reputable led manufacturer has them not ebay or amazon special. The ones I use in my evo are only 41 watt led and they are plenty bright enough. My reverse are 9-16v which is like 310 lumens.

Now I think about it I think you are thinking of lumens not watts. Problems you may have is they may melt the housings. Back to my setup my headlights are low 3300 lumens and my highs are 3900 lumens. and my reverse bulbs and the rest of them bulbs in the tails are 310 lumens.