The answer is yes you can do it. You can edit the melody by first switching from bsq mode to song mode, and then press the >> arrow to measure 13 and record from there. You can record on top (w/o erasing your previous recording) or over it from measure 13. Also, you can set auto punch (S/E) start recording at mesasure 13 and end in wherever.

As for the chord/accompaniment part, you can edit that in the bsq mode with something called chord/acc step mode. In there you can select the measure and edit the chords w/o actually playing it real time.