You can use [String Overrides][1] modules for overriding any string that passed through [t()][2].

Here are some details about this module from its project page:

> Provides a quick and easy way to replace any text on the site.

> Features:

> - Easily replace anything that's passed through t()
> - Locale support, allowing you to override strings in any language
> - Ability to import/export *.po files, for easy migration from the Locale module
> - Note that this is not a replacement to Locale as having thousands of overrides can cause more pain then benefit. Use this only if you need a few easy text changes.


  [1]: https://www.drupal.org/project/stringoverrides
  [2]: https://api.drupal.org/api/drupal/includes%21bootstrap.inc/function/t/7