You can replace all occurrences of a specific string or regular expression with the return value of a BeanShell script if the Return value of a BeanShell snippet radio button is selected in the search dialog box.

You can use this, for example, to convert all tags in an HTML file to lower case, by searching for the following regular expression:

<(.+?)>

And entering the following in the replace text field:

"<" + _1.toLowerCase() + ">"