just a short comment here .. the .mrc files are nothing but .txt files with a different extension.
You aren't REQUIRED to have the .mrc extension .. mIRC will load any text file with any extension. It will load myscript.gar the same as it will load myscript.txt or myscript.mrc (or even myscript.biteme

)
Also, you can save it as a .txt file in notepad and go to it with WinDoZe explorer and highlight the file, then hit F2 and rename it