Normally when you sign the loan paper you also agree with its terms and conditions, i.e. you also agree with the interest rate mentioned in the document. So chances are less that you can alter the rate that you have agreed upon. You can check with the following link for more information and also wait for the experts.
"http://blog.wellsfargo.com/StudentLoanDown/2009/02/can_i_lower_my_student_loan_in.html"