How to change placeholder title of search box?
By using hook_form_alter and/or any of its descendants, you are altering the placeholder everywhere and anywhere that the form occurs.

To isolate specific instances of the form, based on which region they are in, you can use hook_preprocess_page.

For example, in your template.php:

function yourthemename_preprocess_page(&amp;$variables) {
  if (arg(1) == '92') {
     // Set the default value for the form in the header region.
    $variables['page']['header']['search_form']['search_block_form']['#attributes']['placeholder'] = t('abc');

     // Set the default value for the form in the content region.
    $variables['page']['content']['search_form']['search_block_form']['#attributes']['placeholder'] = t('def');
  }
}