This has been around awhile but if you haven't run across it before, you have now!
And you need it, especially since it's a Freebie.
I prefer Metapad to Notepad as a source editor for HTML in IE7 and this does the changing easily, and as often as you want. Use any editor you want. ......and did I mention it's Free?
What we need now is a similar app to change the default "Save as" from mht to html!