Is there a difference between renaming a file to a different file extension by using the DOS prompt vs. renaming the file by highlighting the file icon and changing it right there?

I'm trying to get a program to recognize an mp3 file as a midi file (for a cell phone ringtone), so I renamed filename.mp3 to filename.mid, and it is still treating it as an mp3. Now I know that the mp3 is not "physically" transformed by simply renaming it, but I'm wondering if I try to rename it through the DOS prompt, it may trick the program into thinking it really is a .mid file.

Also, what would the correct syntax be for the command? (I've almost never used DOS before). Thanks!