Yes without a shadow of doubt people can change.
Trust me from personal experience when holding your 16 year old girlfriends hand, on her birthday of all days as she slips away in front of you and dies from cancer changes you.
I'm sure other circumstances would change others, it's maybe not so much change as adjust owing to the new experience, your outlook on life, and the way you are with situations/people.
My bessie mate did 7 years for murder but I trust him 100%.
tabetha