Couldn't find any documentation about this.

I want to have a set of tokens that I can use in any text field. So, I could write %admin anywhere, and if the administrator changes, I won't have to hunt around on the site to find all the places to change his name.

Is there a module that exists for this already, or should I write something custom? I have experience with PHP, although I haven't yet done anything with the Drupal API.