There are artists who started hard and ended up conscious. KRS One comes to mind. Jay Z to a degree. In rock, maybe The Beatles would qualify. Although they never went 'hard' or explicit just more serious from their bubblegum pop beginnings. I'm sure there are others.

But I can't think of any groups or MC's that started conscious or reflective and transitioned into a gangsta or hardcore image.

I wondered about this after listening to Oddisee's Yeezus Was a Mortal Man. Oddisee drops some harsh language (for him) in the song. That whole album was 'harder' than his previous albums (and following ones) so it's clear his audience didn't like the direction his music was headed.

And Das EFX comes to mind too. They started out a novelty or gimmicky act and went street and I don't remember them having nearly the success post-Dead Serious.