559708 Joomla Changes on Account Verification page

I need to add a little piece of code when user verify account, it's when he click on email link activation. So I try to modify redirect, line 83 in /public_html/components/com_users/controllers You can download file from: [login to view URL] Something is wrong because if I add that line 83 when I verify account I don't go to [login to view URL] and also I get error when I try registrer new user. Someone has the solution ? Thanks.