Yes your application for study permit will be rejected since you have an offer letter which is of lesser qualification than your current one. Obviously you can change your tide with proper reasoning through study plan and reference letters.
Because when someone applies for a lesser qualification, VO knows right away that the applicant's intention is something else. Who would want to spend money on education with lesser value than the current qualification? If it was a post graduate certification, you would have no prob as long as it's in IT.