In Sibelius 6 a header or footer could be covered by a new header or footer with erase background switched on. Thus movements or songs could be designed individually all through a long orchestral score or songbook. In Sibelius 7 this doesn't work any longer.
A added some text that crossed a barline in the score. I set erase background true in the Inspector. I then set the item to show in parts only. The background is still visible in the score and should not be, on screen and when printing.