In April of this year I threw a little module together called Engage: F3 that allows site administrators and superusers to easily search for strings of content within their Text/HTML modules and Engage: Publish content on a site. Recently I've taken the time to come up with a new release of the module that provides Search and Replace functionality for the Text/HTML module.
Engage: F3 is a free module available from www.engagemodules.com. (you must be registered/logged in to the site to see the downloads on the Engage: F3 page) Free source code (C#) is available for this module for as well. Feel free to open it up and see how it works!
The module is written in C# and compiled against DNN 4.5.1 meaning it will run against all DNN versions 4.5.1 and above, if you need the functionality for a previous version of DNN feel free to grab the source code and recompile it against an older DNN release.
Example Use Case: You're developing a site at http://test.mydomain.com/ and when you get ready to move to product at http://www.mydomain.com you realize that all of your Text/HTML content has "test.mydomain.com" hard coded into the content! Engage: F3 to the rescue! You can easily search for all instances of that string in your TextHTML modules, and with the new release you can also replace the string with a new value.