Can I change my mind about a career once I started studying? What happens then?

Reaserch
http://careerplanning.about.com/od/careerchoicechan/a/change_quiz.htm
http://careerplanning.about.com/od/careerchoicechan/tp/career_change.htm
http://www.careershifters.org/expert-advice
http://www.canadianliving.com/life/work/10_tips_for_making_a_successful_career_change.php
Information Summary
There are many websites, quizzes, counselors and speaking guidance in which people help you to learn what is the area of study that you like, and what is the best career for you. There are some steps that you should put yourself through to know if this is really what you want and what is the best way to do the change. First you should be 100% sure you want the change of career instead of a change of class or level. Then focus on what new careers are there for you to choose on and narrow all your options until you find the one you want. Finally just to make sure take small courses of your new career to see if it is really what you expect. If you change career nothing bad will happen, its just a waste of your time and money, but if it will bring a greater future and happiness it will be worth it.
New Questions about this topic
1. Is there any course before entering college that gives you a small introduction to the basics of each career to know what are they about?