it is said that alot of people who seek out information on their past lives and are successful will sometimes suffer or gain from that knowledge.

For example a man may journey mentally and be shown some details and events in a past life where he was a violent killer, and when he returns he will retain some of those attributes from his journey.

I read a study that was doen on a man and this is exactly what happened, i cannot remember where it was though, but it was extremely interesting and if i find it i will be sure to post it here for everyone.

I would be interested in seeing some specifics on this topic. I am not sure I am clear as to what you are really saying.

Ok let me give you an example(this is not a true story, just an example!)

A man journeys with his spirit guide to see his past life. In his past life he was an abusive person with anger and violence problems. The man comes back from this experience and the journey has almost sparked these personality attributes in him and he carries these attributes back to his current form.

Now the man who was once a kind calm relaxed gentle man, is now suffering from short-temper and anger problems.

The study was showing how re-uniting someone with their past lives can spark some of their old qualities. Not necesarially bad ones either, intelligence, sense of humor, passive etc etc.

does hypnosis could have a similar effect? i mean regressing in the past

there is something called hypnotic regression that helps u recall stuff that u wudnt otherwise do when u r awake.