Globally increase #maxlength attribute of textfield (form api)

Question

I have thousabds of field for admin to edit data which is saved in db from mobile app. i can fetch those data into text field while editing but drupal having default #maxlength of 128 character but in my case i have data field which is more than 128 character so its creating problem while saving those data in db. Pls help.. i tried to hack drupal core by writing code in from.inc.

function theme_textfield($variables) {
   $element = $variables['element'];
   $element['#attributes']['type'] = 'text';
+  // Remove maxlength when it's too long to be useful. 
+  if ($element['#maxlength'] >= 128) {
+    unset($element['#maxlength']);
+  }
   element_set_attributes($element, array('id', 'name', 'value', 'size', 'maxlength', 'placeholder'));
   _form_set_class($element, array('form-text'));

but it dint work. pls tell me any solution.