If I read your question right, yes you can open the midi file in BB and or Real Band, and change to what ever chord pattern you want to. However, that doesn't mean it's going to sound good, but different. If you don't know what you're doing here, which I'm sure you do, then you can really mess up the song. To keep changes of course, you would have to save the file either back to midi or a bb extension. Also, you are limited to 4 chords per measure, unless you pull a Notes Norton and break up the measures. A majority of songs nowdays Have more that 4 chords per measure. Hope this is helps and is what you asked for.