HTML editor for Internet Explorer can be changed using the Internet Options menu. The Internet Options is available under the tools menu on the right hand side of the Internet Explorer.
In the Internet Options window, click on the Programs tab and navigate to HTML editing section.
Using the HTML editor dropdown you can change the HTML editor used by Internet Explorer 9 (IE9). This will be used by the Internet Explorer for editing all the HTML files. For example, you are big fan of Notepad as want to use that as your default html editor then you can pick that from the HTML editor drop down list.