As long as the string or text is passed via [t() function][1] you can override it using [String Overrides][2] module. Here is a quote from module's project page:

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

**UPDATE**

You can also use [Variable][3] module. Quote from project page:

 > ... provides a registry for meta-data about Drupal variables and some extended Variable API and administration interface.
 >
 > This is an API module so it must be installed only when other modules require it.

  [1]: http://api.drupal.org/api/function/t
  [2]: https://www.drupal.org/project/stringoverrides
  [3]: https://www.drupal.org/project/variable