Complete crap.

There's no way it can mess with your brain; the same chemical reactions that occur 24/7 normally still happen. The only difference is that you're conscious during a dream, and can consciously control the dream if you choose.

As for changing your personality, it can. All experiences in life can change your personality, and lucid dreaming is no exception. But it is what you make it. Conscious dreams don't change anything, just what you do with them

Sometimes people have traumatic experiences in life and use them to improve their outlook on life. Sometimes people have great experiences in life that end up making their personality worse. It's up to you really.