First and foremost, thanks for the suggestions and how to hyperlink.
I did however watch Code Geass and even read some of the spin-offs mangas of it. As for knight run I'm currently reading it, awesome manhwa but sadly it isn't on batoto anymore and the offical scans are way behind... I will however, check out Hanged Doll, Black Lagoon and Destroy and Revolution.
the thing with what you want is, its kinda spoil sensitive. Most of these changes happen in the end, and you have to read the full manga for it to finally happen, and might drop it before it happens. meanwhile we cant tell you who is gonna change, cause that will take all the fun out of it xD
Oh I'm fully aware that this can be very spoiler sensitive. And as you said many times this happens at the end. Which in a sense a bummer since sometimes tha just begs for a continuation of some sort. And this doesn't help there is also many cases of anti-heros or outright villian protagonist from the very beginning.
I'm just suprised that there isn't that many series where the protagonist start out good then becomes a villian midway and then perhaps in the end of the story becomes good again, or stays evil or die as a villian. There are so many different outcomes. This seems to be the case that the trope doesn't seem to be that very popular nowadays. I know there are many that serves as a backstory of character(s) but that is not really what I'm looking for. I'll still take it.
I'll still wait and see what other recommendation you guys will give me before calling it a day.