There are multiple different ways to do this which you've probably found.

You could use Melody menu | Edit Melody Track | Form | Copy 1st Chorus to All Song (command+shift_Z). Then, from the same submenu, Kill Melody from Middle Choruses.

Note also that when you change the number of choruses in your song Band-in-a-Box does automatically adjust copy the melody if you answer Yes to the "Adjust Melody track" question.

Bar settings (mute / back to normal) (F5 at current bar) can be helpful as well.

Andrew
PG Music Inc.