You'd have to "select" the portion of the MIDI to change and delete that section
where you want the "groove" to change and then add the "new" groove to just
that section...do this as many times as you want the groove to change...
that will create the song with the "feel" that you want...then, on playback, you'll
be hearing the "entire" song with both (or however many) groove changes the song
has.